Marcus Forrester is the biological son of Donna Logan and Justin Barber; he was adopted by Jerry Walton and raised with his adoptive brother, Carter Walton, in Texas. Marcus saw a newspaper photo of Donna with her new husband, Forrester Creations' co-founder Eric Forrester, and headed for Los Angeles, posing as a caterer at the memorial service of Donna's brother, Storm Logan. Marcus presented his birth certificate to Donna, who admitted giving Marcus up for adoption; Marcus was initially angry but soon developed a relationship with his mother. Marcus began working in the Forrester shipping department, where he met Steffy Forrester. Marcus and Steffy dated, though her family disapproved.

Marcus panicked when Owen Knight, the private investigator who located Donna for Marcus, arrived and demanded a $2,500 bonus Marcus couldn't afford. Later, when Eric had a heart attack and lapsed into a coma, Marcus suggested Eric had been poisoned and accused Owen, knowing Owen had a yen for Donna. Marcus and Owen mended fences after Owen discovered that Eric's former sister-in-law, the unstable Pam Douglas, was the culprit.

Marcus opened a crate meant for Donna and was bitten by a poisonous snake that Pam had packed inside. After Marcus recovered, he was thrilled when Rick Forrester offered him an overseas opportunity at Forrester International, unaware that Rick wanted Marcus' girlfriend Steffy for himself. Marcus came home and proposed to Steffy at the Forrester cabin in Big Bear, saddened to learn that Steffy had developed feelings for Rick in Marcus' absence.

Marcus was legally adopted by Eric just as Justin came to town, not knowing Marcus was his son. Once Marcus and Justin found out they were related, Marcus got his parents' backstory: Donna and Justin dated in high school, and Justin never knew that the real reason she suddenly left for Europe was because she was pregnant. Marcus accepted Justin and considered reverting to his true surname of Barber, but ultimately kept the name Forrester.

Marcus attended the high school dance of his cousin, Hope Logan, where he befriended Hope's boyfriend, Oliver Jones, and fended off advances from Steffy. Marcus covered for Oliver, who gave down-and-out designer Amber Moore a place to stay; Marcus and Amber became "friends with benefits," but when Amber got pregnant, Marcus was relieved to hear he wasn't the father. Marcus' new relationship with coffee house owner Dayzee Leigh was cut short when Marcus had to take an assignment in Paris; when he got back, he was annoyed to see Dayzee had moved on with Thomas Forrester.

Marcus happily attended his parents' wedding and met Justin's Genoa City cousin, Olivia Barber, but soon Marcus had to accept that Donna and Justin had only married to give Marcus a family and were better off as friends. Despite Amber claiming that Caucasian Liam Cooper was the father of her child, she gave birth to an African-American baby, whom Marcus knew was his; he gladly took responsibility and named the child Rosie after Amber's full name of Ambrosia. Marcus reconnected with Dayzee, gently refusing Amber's request to become a family with Rosie. After Marcus proposed to Dayzee, Marcus received a call from Justin, who had unintentionally "pocket dialed" him, and overheard Justin and his boss, Bill Spencer, Jr., discussing a plot to prevent Liam's marriage to Hope. Marcus confronted Justin but got nowhere, uncomfortably deciding to keep quiet even as Liam and Hope flew to Italy for their wedding.

Marcus got over a case of cold feet before his own wedding but accidentally hit Dayzee's friend Anthony with his car because he was texting while driving. Marcus was jailed right after marrying Dayzee, but freed when Thomas and his girlfriend, Caroline Spencer, found out Marcus had only hit a pothole while someone else ran into Anthony. Marcus settled into married life with Dayzee and greeted his visiting adoptive brother, Carter. When Dayzee confessed that she had helped find a home for the child of Maya Avant but couldn't be sure money didn't change hands, Marcus had attorney Carter study the adoption papers. Marcus helped Carter and Dayzee track down the child for Maya and learned that the girl had perished in a car crash with her adoptive family.

Marcus got Carter a job at Forrester Creations, then strutted his stuff on the runway modeling sleepwear to benefit Caroline's cancer foundation. Marcus then spent an extended period in South Africa on Forrester business, keeping in touch with Dayzee via video chat. Marcus hasn't been seen since 2013, when Dayzee and Rosie joined him in his new country.