Mark is born off screen in 1996 after his parents have a one-night stand. Michelle only tells her brother, Mark Fowler, who the father is, before emigrating to the US. Michelle is unable to attend the funeral of her father, Arthur Fowler, when she gives birth to Mark. In 2016, Phil Mitchell contacts Mark after finding a letter in his wife's Sharon Mitchell's bag, who is Michelle's best friend, from Michelle addressed to his and Grant's mother Peggy Mitchell, who has since died, about Mark. Sharon and Martin Fowler, Mark's uncle, worry about Grant learning the truth and convince Phil not to tell him, and Michelle has told Mark that Phil is lying because he is an alcoholic who hates her. However, Mark arrives at Martin's flat. Mark goes to see Phil and asks if what he said about Tim not being his real father is true, but Phil has agreed with Sharon to not reveal the truth, so he denies even speaking to Mark. Mark decides to stay in Walford to get to know his family.
Mark is quick to join the market with Phil's ex-wife Kathy Sullivan, who is the aunt of Michelle, Mark and Martin, and makes fast friends with Shakil Kazemi, who seems envious of Mark's popularity with women. Mark takes a liking to Courtney Mitchell, not knowing she's his half-sister, and both admit that they like each other. Their cousin Louise Mitchell tells Sharon about them, prompting her and Michelle's cousin, Ian Beale, to find them. Sharon, Ian and Phil find out nothing happened between Mark and Courtney, but Sharon and Ian book him tickets to return home. Mark explains that he feels at home in Walford and feels a connection with Courtney. When Courtney is a victim of a break-in, Mark comforts her, but is then confronted by Grant who assumes Mark is attacking her. Grant learns that Mark is Michelle's son and shares passing comments of his dislike of her; Mark shares that the feeling is mutual.
When Ben Mitchell and Jay Brown are kidnapped by Paul Coker's killers, Mark and Grant go to find them and they bring Ben back, but leave Jay behind. Phil tells Grant that Mark is his son. Grant stops Mark and Courtney kissing but agrees that Mark is better off not knowing the truth, however, Jane Beale encourages Grant to tell Mark, as Mark can then make up his own mind, so Grant invites Mark to join him for a drink and a chat. Grant talks to Mark about Michelle and Tim, and Mark says he would not want a different father despite their differences, so Grant decides not to tell Mark the truth. As Mark is about to leave, he tells Sharon he worked out that Grant is his father and Sharon confirms it. However, she urges Mark not to ruin his life by getting involved with Grant. Mark then leaves to return to his mother and Tim in the United States.
When Michelle returns to Walford later in the year, she tells Sharon that Mark has a girlfriend and has moved out. However he is not speaking to Michelle because she has broken the law in Florida for having a relationship with a 17-year-old student Preston Cooper. A year and a half later, Michelle leaves Walford and goes to visit Mark and Vicki in Australia to reconnect with them.