A resident of Atlantic City, Margaret is an Irish immigrant of poor, rural background whose relation to the family she left there as a teenager is non-existent. She is the widow of an abusive husband, Hans Schroeder, and has two surviving children, Teddy and Emily. Although smart and with an interest in politics which led her to join the Women's Temperance League and the League of Women Voters, Margaret's main motivation is to secure a source of income that can provide for her and her children and will put back her ideals if she needs to achieve it. Her fortunes greatly improve when she becomes the domestic partner and eventual wife of Atlantic City crime boss Nucky Thompson, but the guilt stemming from his actions soon grows to be too much to bear for her.
Margaret was born Margaret Catherine Sheila Rohan in County Kerry, Ireland circa 1893 and retains a strong Irish accent. She was the first daughter and second child born to a family of poor Catholic farmers. She has an older brother, Eamonn, and three younger sisters: Nuala, Bethany (known as Beth), and Aylesh. Her father was an alcoholic, at one point selling the family cow to pay for his addiction, and often got into arguments with her mother.
Margaret's father died shortly before or after the birth of Aylesh in 1909, when Margaret was 16. Left in poverty and having to raise three young girls, the family began to save money to send Eamonn to America for better opportunities. Margaret also began to work as a maid in the house of a rich, Protestant barrister named Mr Walton. The place had a large library and according to Margaret her employer let her read whatever she wished, George Sand's novels being an example. This way, Margaret acquired an education far superior to what her upbringing could have afforded. At the same time, she began a romantic relationship with the attorney's son, Douglas, and became pregnant - changing Margaret's life forever.
Margaret was unable to conceal the pregnancy from her family and taken to see the local priest for advice. When inquired she refused to name the baby's father and claimed that she had been raped (which wasn't true) but she was not believed. The priest decided that she should be sent to a Magdalene Asylum to reform her morals. Margaret could not bear this fate and after her brother decided to not interfere in her favor she stole her mother's savings intended for him and used the money to emigrate to America herself. She left Ireland on the passenger ship Haverford from the port of Galway on 27 September 1909, which after a detour in Southampton, England, arrived on New York City. Margaret miscarried during the voyage in steerage, and her Ellis Island immigration file includes a medical assessment containing these details. Margaret never wrote back to Ireland and only kept in touch with a fellow immigrant cousin, Martin Hennessey, from whom she knew years later that her mother had died.
Some time later she moved to Atlantic City and married baker's assistant Hans Schroeder, an immigrant from Germany. Unlike Margaret, Hans managed to lose his accent and would criticize his wife for sounding like if she had just got off the boat. The two had two children: Teddy Schroeder, born in 1914, and Emily Schroeder, born in 1916. At the start of the series in January 1920, Margaret is pregnant for a fourth time and lives with her family in a small, humble house in the Fourth Ward of Atlantic City. She is a member of the Women's Temperance League, due in part to the controlling, abusive nature of her alcoholic and gambling-addicted husband.
- Main article: Margaret Thompson Season 1
Margaret attends a meeting of the Women's Temperance League the night before Prohibition is made official nationwide in the United States, on January 16, 1920, and hears Atlantic County Treasurer Nucky Thompson give a speech in which he claims to have hunted rats as a child to feed his starving family during a blizzard in 1888, being unable to rely on his alcoholic father. Margaret is moved by the story and goes the next day to Thompson's office in the Ritz-Carlton Hotel to ask for a job for her husband, Hans Schroeder, a part-time baker's assistant, alcoholic, and gambling addict. Hans is out of work until the tourist season and the children have no shoes for the winter. Despite her reluctance, Nucky gives her money to go through the winter rather than seeking a job for Hans and asks his driver, Jimmy Darmody, to take her home. Hans observes the unusual sight and, after finding the money under the mattress, concludes that Margaret has gained it through prostitution, even though she is visibly pregnant. Hans beats her in front of the children and takes the money to gamble at Lolly's Casino. Nucky sees Hans, beats him, and has him tossed out of the place. Hans then goes home and beats Margaret so hard that she miscarries and has to be hospitalized. When Nucky gets word of this, he orders his brother Eli to kill Hans and use him as a fall guy for the Hammonton hijacking, then pays Margaret again to keep her quiet. She refuses the money, however, and returns it to Nucky saying that it weighs too much on her conscience. Prohibition Agent Nelson Van Alden also begins an investigation about the hijacking and after meeting Margaret becomes sexually obsessed with her.
In order to help Margaret, Nucky forces Isabelle Jeunet to fire her assistant at La Belle Femme clothing shop and hire Margaret in her place. The new boss makes no attempt to hide her disgust for the imposition. Margaret delivers a dress to Lucy Danziger during Nucky's birthday party in February and he is impressed when she is able to hold a discussion with mayors and senators alike; the two then dance together. In March, Margaret recognizes Jim Neary unloading beer for the Order of Ancient Celts annual Saint Patrick's Day dinner behind her house and, after failing to charm Nucky further, she denounces Neary to Van Alden, who closes the place and arrests him. Nucky observes Margaret singing along with the other members of the Temperance League and comes to her house late in the night to tell her that he doesn't like playing games. He kisses her and the two end having sex in the hallway.
Lucy confronts Margaret at the clothing shop and she resigns. Nucky moves her and the children to a house in a neighborhood inhabited by other kept women. Margaret asks Mrs McGarry for advice and she tells her that she is free to do as she chooses, but hands her a pamphlet on birth control and encourages her to read it. In June, Nucky leaves for the Republican National Convention in Chicago and while in there he phones Margaret at night and tells her that his brother has been shot and she needs to retrieve a ledger from his suit for safekeeping. Margaret opens the ledger and discovers that it is completely detailing Nucky's illegal liquor trade. One month later, a man shoots at Nucky and Margaret while they are walking on the Boardwalk.
Van Alden visits Margaret and tells her that Nucky killed her husband. While she turns down the agent's offer to "save" her, Nucky uses her to back his candidate for Mayor Edward Bader before the League of Women Voters and she later happens upon him talking to Annabelle, one of his former mistresses, leading her to wonder if Nucky cares about her at all. They have a discussion where Nucky denies his part on Hans's murder and criticizes her for defending her abuser and using lysol to deny him a natural son, after which Margaret leaves the house. She later learns that Nucky lost his first son tragically, and after getting the rag in the Halloween Irish dessert barmbrack (which according to tradition means she'll be destitute) she returns to Nucky's side. The two reconcile in time to hear that Republican Warren G. Harding has been elected President of the United States.
- Main article: Margaret Thompson Season 2
Margaret and Nucky move to an upper-class family house in Margate. When Nucky is arrested on February 13, 1921, she disguises herself as a poor woman and snatches the incriminating ledger right under the nose of the New Jersey State Police, burning it later. The couple disagrees about how to deal with their current situation: Nucky thinks that it is best to pretend that everything is normal and tells Margaret to give a raise to the house staff; Margaret thinks that economic hardships are coming and lowers the wages without telling Nucky, keeping the money for herself.
Margaret learns from the Pinkerton's National Detective Agency that the siblings she left in Ireland have since moved to Brooklyn, New York City and visits them. She returns the money she took as a teenager to Eamonn, who initially takes it, but when he sees that she is trying to build a relationship with the younger sister, Aylesh, Eamonn (who thinks that Margaret is a bad influence) gives the money back and tells her to not contact them again. Distraught from the rejection, Margaret succumbs to her sexual attraction to Owen Sleater, Nucky's new driver and bodyguard from Ireland, and they sleep together in the house—albeit after telling him that it is only a one time thing and will never speak about it again. Nucky is shot through the hand and Margaret, worrying about their safety, pleads him to leave the criminal life. Nucky resigns as County Treasurer soon after.
Emily is paralyzed by polio and Margaret sees it as divine punishment for her own sins. She donates her jewels and the money she has collected to Saint Finbar's Church, and when she is subpoenaed by Assistant US Attorney Esther Randolph to testify about Nucky's criminal enterprises and his role in Hans' murder, she considers it to Nucky's disbelief, since a conviction could put him in the electric chair. Nevertheless, Nucky puts the land in which he has invested most of his fortune as part of a speculation scheme under Margaret's name to keep it away from the government if he is convicted. Margaret meets with Randolph but after seeing Nucky encouraging Emily to walk with her crutches, she decides that life with him is the best for the children. She makes a complete confession to Father Ed Brennan and marries Nucky in Saint Finbar's, making impossible for Randolph to force Margaret to testify because of spousal privilege. As Nucky kills or scares the rest of the witnesses from testifying, the case flounders and he walks as a free man. That same night Nucky kills Jimmy, his former protegé who had led the attempt to incriminate him, and lies to Margaret saying that he has left town to reenlist in the US Army. Margaret sees through his lie and punishes him by deeding Nucky's land to the Church.
- Main article: Margaret Thompson Season 3
Margaret's decision ends her relationship with Nucky in all but name. By December 31, 1922, she lives with the children in Margate and Nucky in his suite at the Ritz-Carlton, although they continue to act like a loving married couple while in the presence of others.
Margaret is a member of the board of Saint Theresa's Hospital, a Catholic hospital built with the money gained through the land donation. During a tour of the hospital, she runs into a pregnant woman, Edwina Shearer, who is profusely bleeding and then faints in her presence. A young doctor, Douglas Mason, informs her that the woman suffered a miscarriage for drinking raw milk and blames the lack of a prenatal care program in the hospital for the incident. However, when she tries to discuss it with the medical director, Dr. Robert Landau, he reacts with hostility. Margaret takes the task of opening a prenatal care clinic upon herself and during the ceremony that rewards Nucky for the land donation with a membership of the Papal Order of Saint Gregory the Great, she tricks Landau into asking Bishop Norman for one. Margaret then assists Mason with the prenatal care classes, attempting to sidestep Catholic censorship until they are cancelled by order of the Bishop in June.
Margaret discovers that Nucky has a mistress, Billie Kent, and decides to re-initiate her own relationship with Owen. She also learns that Shearer didn't have a miscarriage but aborted the baby on purpose. Shearer then pleads with Margaret to provide her with a diaphragm. When Gyp Rosetti blows up Babette's in an attempt on Nucky's life, he injures Nucky and kills Billie. Margaret then helps Nucky put himself together before meeting with other mobsters to help him in the war against Rosetti and his protector, Joe Masseria, but makes secret plans with Owen—being now pregnant with his child—to leave Nucky. However, Nucky sends Owen to kill Masseria, who instead kills Owen and sends his body back to Nucky in a box. When Margaret sees it she breaks down crying, revealing their affair to Nucky, and she leaves with the children for Brooklyn where she has an abortion. Nucky wins the war against Rosetti and offers Margaret to go back to him, but she refuses, preferring to live in poverty.
By 1924, Margaret has moved to New York and began working at Conors & Gould, an investment firm.
- Hans Schroeder: Husband (deceased)
- Nucky Thompson: Second husband (deceased)
- Elias "Eli" Thompson: Brother-in-law
- Emily Schroeder: Daughter
- Teddy Schroeder: Son
- Eamonn Rohan: Brother
- Nuala Rohan: Sister
- Bethany Rohan: Sister
- Aylesh Rohan: Sister
- Anne Thompson: Niece
- Martin Hennessey: Cousin
- Regina: Former pet
- Owen Sleater: Lover, Nucky's driver (deceased)
- Katy: Ex-employee, former housemaid
- Lillian: Governess for children
- Pauleen: Ex-employee, former cook
- Eddie Kessler: Nucky's assistant (deceased)
- Harlan: Ex-employee, Nucky's valet
- Prudence: Housemaid
- Phillip: Footman
- Nucky's butler: Butler
- Gareth Murray: Bodyguard (deceased)
- Richard Harrow: Former bodyguard (deceased)
Saint Theresa's Hospital staff
- Dr Robert Landau: Medical director
- Dr Douglas Mason: Saint Theresa's doctor, ally
- Sister Agnes: Saint Theresa's nurse
- Douglas Walton: First lover
- Mr Walton: Former Employer
- Father Brennan: Priest
- Cornelia Predock: Neighbour
- Annabelle: Former neighbour
- Nan Britton: Mistress of Warren Harding, friend
- Edith Mauer: Former neighbour
- Mrs McGarry: Leader of the Atlantic City Women's Temperance League
- Lucy Danziger: Nucky's mistress, former rival
- Billie Kent: Nucky's mistress, rival (deceased)
- Arnold Rothstein: Investment accomplice, Landlord (deceased)
- (To Nucky) "I would be honored to name my child after you." ("Boardwalk Empire")
- "I've been lectured to a great deal today by men who speak boldly and do nothing."
- Lucy: "So what is the point?"
- Margaret: "...that maybe your cuny isn't quite the draw you think it is.................I quit." ("Family Limitation")
- "It's three-thirty bearcat. Get a wiggle on."
- "You did what you wanted, Peg. You always have." (Eamonn Rohan on Margaret) ("Peg of Old")
- "You're honest are you?... Never take more than you need. Never talk back to the priest or the boss or the policeman. Never question. Never make a fuss. Never dare to stand up for me... your own flesh and blood. Who begged you for help when she'd nowhere else to turn. And you're proud of it." ("Peg of Old")
- "The spoons were too long..."
- "What do they say on Broadway? The show must go on." ("Bone for Tuna")
- "He has a mistress. An actress in New York. He's there half the week. We hardly talk. He's involved in doings I can't bear to think about. He blames me. I blame him. And I feel like... the life is being pressed out of me." ("Sunday Best")
- (To Joe Kennedy) "Here's an experiment for you.Think about the things you want in life, and then picture yourself in a dress. You've just made some money." ("Eldorado")
- Nucky: "This is only money. It doesn't mean anything."
- Margaret: "Yes it does" ("Margate Sands")
|Season one appearances|
|Boardwalk Empire||The Ivory Tower||Broadway Limited||Anastasia|
|Nights in Ballygran||Family Limitation||Home||Hold Me in Paradise|
|Belle Femme||The Emerald City||Paris Green||A Return to Normalcy|
|Season two appearances|
|21||Ourselves Alone||A Dangerous Maid||What Does the Bee Do?|
|Gimcrack & Bunkum||The Age of Reason||Peg of Old||Two Boats and a Lifeguard|
|Battle of the Century||Georgia Peaches||Under God's Power She Flourishes||To the Lost|
|Season three appearances|
|"Resolution"||"Spaghetti and Coffee"||"Bone for Tuna"||"Blue Bell Boy"|
|"You'd Be Surprised"||"Ging Gang Goolie"||"Sunday Best"||"The Pony"|
|"The Milkmaid's Lot"||"A Man, A Plan..."||"Two Imposters"||"Margate Sands"|
|Season four appearances|
|"New York Sour"||"Resignation"||"Acres of Diamonds"||"All In"|
|"Erlkonig"||"The North Star"||"William Wilson"||"The Old Ship of Zion"|
|"Marriage and Hunting"||"White Horse Pike"||"Havre De Grace"||"Farewell Daddy Blues"|
|Season five appearances|
|Golden Days for Boys and Girls||The Good Listener||What Jesus Said||Cuanto|
|King of Norway||Devil You Know||Friendless Child||Eldorado|