Mo was born in 1936, the eldest child of an impoverished family in the East End of London.
At the age of 14, she becomes pregnant, following a one-night stand with Stuart Mullins, a ticket collector for the Waltzer ride at a fairground in South London, and gives birth to their daughter Vivienne the following year in 1951.
Best friends with Pat Harris, Mo falls for Pat's older brother Jimmy and after a whirlwind romance they marry in 1959 and go on to have two children of their own: Billy and Jean. However, Pat threatens to disrupt their marriage due to her alcoholism and eventual prostitution, which diverts Jimmy's attention away from Mo and onto Pat; this results in Mo beginning an affair with Pat's pimp Tony Cattani in 1963. When Pat discovers them together she informs her brother but Mo denies Pat's accusations and as a result Jimmy disowns Pat and they move away to Lewisham. Jimmy later dies of cancer in 1979. His final wish is to make amends with his sister Pat but instead Mo neglects to inform her of both his death and his funeral.
Life in Walford
Mo, who previously lived in Walford, returns there after almost forty years away, with her son-in-law, Charlie Slater and granddaughters, Lynne Slater, Kat Slater, Little Mo Morgan and Zoe Slater. Mo's rivalry with her former best friend Pat Evans arises, but they reconcile at the grave of Mo's former husband and Pat's brother, Jimmy Harris. Much of Mo's time is spent selling poor quality stolen goods and she trades with Fat Elvis. She is assisted by Mickey and Darren Miller and for a while sets up a sex chatline. She also works with Charlie's great-niece, Stacey Slater on her market stall, selling clothes. She has a brief relationship with Bert Atkinson but ends it because Bert is also seeing her friend, Ina Foot. They reconcile, but break up again when Bert's ex-wife, Evie Brown, arrives in Walford, terminally ill. Mo begins selling cigarettes that she bought in Spain and two of her customers turn out to be Revenue and Customs officers. She is sentenced to 100 hours of community service, for tax evasion. After Stacey marries Bradley Branning, Mo tries to sell their wedding gifts.
Mo sees Charlie's partner, Brenda Boyle, embracing another man at the tube station, but the man is Brenda's brother, Clive Robinson. Brenda reveals to Mo that she is moving to Madeira with her family and Mo convinces Charlie not to let her go. However, Brenda and Charlie leave together, leaving Mo devastated. She begins drinking heavily and protests against the sale of Charlie's taxi. Charlie returns to Walford with a woman called Orlenda, but Mo does not trust her. Orlenda leaves, after admitting she was scamming Charlie but returns his money. Mo takes charge of a children's nativity play but fails to keep the children under control. In a raffle, she wins Max Branning's car, but sells it, to Max's dismay. When Archie Mitchell is murdered, Mo starts a betting circle on who killed him. She runs when she sees a police officer, but later, another officer appears behind her and she asks him if he wants to place a bet. She goes on holiday to Spain with Fat Elvis and when she returns, she is surprised to discover that Bradley is dead. Mo attempts to sell Lucas Johnson's bibles to the public, as gruesome souvenirs of the killer. Her insensitivity gets her thrown out of The Queen Victoria public house. Mo receives a phone call from Kat, who wants Zoe's birth certificate. Mo meets Kat at a café and gives her the certificate. Kat admits to Mo that she conned a man and needs a new identity. Kat also lies to Mo, claiming that her husband, Alfie Moon is dead. Mo persuades Kat to come home and Kat reluctantly agrees, but when they get home, men are waiting for Kat and her money. However, Alfie sends them away. Mo is shocked to learn that Kat is pregnant and Alfie is not the father. When Kat goes into labour, Mo delivers her son, Tommy Moon, on the floor of The Queen Vic's barrel store. On the same day, Ronnie Branning gives birth to a baby boy, James Branning. On New Year's Eve, Ronnie finds that James has died and she swaps him with Tommy. Alfie and the family find the deceased baby and believe it is Tommy.
After Kat blames Charlie for Tommy's death, Charlie decides to go and live with Lynne, despite Mo begging him not to go. Left living alone, Mo asks Kat if she can move into The Queen Vic and let No. 23. Kat refuses initially but later agrees when Mo reminds her that she never complained about living with Kat's bad habits. Mo continues with her dodgy deals while staying at the pub, including persuading Jean Slater to serve "turkey" for pub lunches, which turns out to be swan meat. When a benefit fraud officer declares that Jean has been illegally claiming benefits while working at the pub, Mo admits to Jean and Kat that she has been claiming benefits in Jean's name. Jean agrees to take the blame, as Mo has previous convictions. When Mo learns that her old enemy, Pat, is terminally ill, she visits her in hospital and they end their long-standing feud. When Pat later dies, Mo returns Pat's Miss Butlin's sash, that she stole years ago, out of jealousy. When Mo learns that Charlie has suffered a stroke, she leaves Walford to look after him. Several months later, Jean visits them and Mo returns to The Queen Vic when she believes that Jean is hiding something from her. Her suspicions are confirmed, when she discovers that Alfie is allowing Roxy Mitchell (Rita Simons) to stay in The Queen Vic. Mo continues to disapprove of Roxy's presence in The Queen Vic, after Kat and Alfie split up. It is later revealed that Mo has rented a villa in Devon, owned by "a mate".
Mo returns to collect rent from Kat, Michael Moon (Steve John Shepherd) and Alice Branning (Jasmyn Banks). She demands Alice pays by the end of the day, or she will evict her. Kat later convinces Mo to give up her keys to the house. Three months later, Jean discovers that Mo is stealing vegetables from the Walford allotments and Mo convinces Jean's new partner, Ollie Walters, a police officer whom Mo knows, not to report her, as she is Jean's family. At Christmas, Mo and Charlie visit Walford, where it is revealed that Kat is pregnant with twins. Two months later, Alfie calls Mo, after dealing with some serious family issues, raised by the re-appearance of Stacey after a four-year absence, to which Mo plans to spend more time in Walford to support her family. Mo is delighted when Kat and Alfie's twins, Bert and Ernie Moon are born, but the family's joy is cut short when a fire starts at their house and when it reaches a supply of knock-off hairspray, which Mo had intended to sell, a huge explosion destroys everything that they own. Kat is badly injured and Mo is wracked with guilt, briefly moving in with Masood Ahmed, before taking an extended holiday in Lanzarote with Charlie.
Mo returns to Albert Square and is shocked to discover that Alfie and Kat have, once again, separated and that her family are struggling, financially. Mo reveals to a destitute Kat that she inherited money from her uncle, Harry, who had raped her as a child. Kat turns the money down, so Mo secretly has the money transferred to her own account, pretending to be Kat. When Kat discovers this, she is livid and burns the money in the street. Kat and Alfie reconcile and after winning the jackpot on a scratch card, plan to move to Tenerife. At their leaving party, Mo shows a stunned Kat an engagement ring, revealing that she has accepted a marriage proposal from her longtime business associate and romantic interest, Fat Elvis. Shortly after Kat and Alfie's departure, Mo and Fat Elvis leave for Greece. When Mo returns alongside Charlie, she reveals that Fat Elvis has left her. When Kat learns she had also given birth to a boy along with Zoe, she realises that Mo knew about the secret, so angrily demands the truth from her. During the argument with Mo that ensues, Charlie suffers a heart attack in front of Mo, Stacey and Kat. After suffering from a cardiac arrest, Charlie dies, which devastates the family. After attending Charlie's funeral, Mo moves to Kent to live with her granddaughter Belinda Peacock as Kat cannot forgive her for having her son adopted. When Belinda moves to Walford after her marriage ends, Mo's whereabouts are not mentioned.
Mo returns to Walford, telling Stacey that Kat has died. They raise funds for Kat's funeral, while Mo avoids answering her phone or the door. A coffin is donated and Mo calls Fat Elvis saying she has a coffin for sale. Jean later arrives, saying that Kat is alive. It emerges that Mo lied to raise money as she has financial troubles. Kat returns to Walford and is confused that The Queen Vic is holding a benefit night for her and she is annoyed with Mo, but is forced to hide when Ian visits with the raised money. Annie Pritchard, the daughter of Terry, who Mo conned, arrives to get his money back, but the family fool her into believing Mo has died and offer to pay the money. Kat, Stacey and Mo arrive at The Queen Vic and attempt to maintain that Mo made a mistake; Mo also fakes a heart attack and bar fight soon starts. The family find out that Mo took £300 for the money and when the family go to return it to Mick Carter, Mo sneaks off and encounters Annie, who injures Mo. Jean repays the money, and Stacey tells Mo she must stay until she pays Jean back. Mo claims to have psychic abilities as a way to make money but she is listening into people's conversations with recording devices. Kat starts a cleaning business and Mo is forced to join her, but she does not work hard and steals from the employers.
"Turn that ruddy noise off!" - to Garry Hobbs.
"I hope you're not the flamin' stripper!"
"Where's Leonardo DiCaprio when you need him?"