Marcus arrived in L.A. in 2008 in search of his birth mother, Donna Logan, and he revealed his identity to her after working as a caterer at Storm's memorial service. At first, Donna denied having a child, but ultimately mother and son shared an emotional reunion, though Marcus was still angry that she had given him up. Donna struggled with sharing the truth with Eric, since she feared causing a scandal for the Forrester family, which led to further conflict with her son. Donna secured Marcus a position in the shipping department at Forrester Creations so both she and an unknowing Eric could get to know him better.

Marcus and Donna's bond slowly grew, and Brooke and Katie readily accepted him as their nephew. Marcus befriended Steffy, who stumbled upon Marcus' birth certificate and learned of his parentage. She agreed to keep his secret, but Phoebe overheard them and blabbed to Ridge that Marcus was Donna's son. Ridge, Thorne, and Felicia tried to use the truth about Marcus to drive a wedge between Eric and Donna, but everyone was surprised when Eric supported Donna and welcomed Marcus into the family. Marcus and Steffy fell in love, despite her family's disapproval.

Owen, who was the private investigator Marcus had hired to find Donna, demanded cash from Marcus in exchange for financing Marcus' trip to L.A. Marcus was suspicious of Owen's motives, especially when Donna offered to cover Marcus' debt and hired Owen as her assistant. When Eric suffered a heart attack, Donna assumed control of Forrester Creations and named Marcus the head of the shipping department. Marcus found evidence that someone had poisoned Eric, and he suspected it was Owen. The men ended up in a fistfight, but a mentally unstable Pam was eventually revealed to be the culprit.

Marcus was bitten by a venomous snake that Pam had sent to Donna. He made a full recovery after spending a night in the hospital, but the incident made Donna and Steffy each realize how much Marcus meant to them. Marcus supported Rick when Eric made Rick president of Forrester Creations, and he was thrilled when Rick gave him the opportunity to work in the Paris office, unaware that Rick's motive was to cause a rift between Marcus and Steffy, so Rick could woo her himself. Marcus returned the evening of Ridge and Brooke's engagement party, and he was livid when Steffy informed him of Rick's true intentions. He consoled Steffy after Phoebe died in a car crash.

Marcus whisked Steffy away to a weekend at Big Bear, oblivious to the feelings she'd developed for Rick. She was shocked when Marcus proposed at the cabin, but she explained that things had changed since Phoebe's death, and she ended their romantic relationship. The pair remained friends, though Marcus' attitude toward Rick soured when he learned of Steffy and Rick's romance. The police questioned him when attempts on Rick's life were made, but he was never arrested.

Donna was shocked when she learned that Bill's right-hand man was Justin Barber, Marcus' biological father. Donna approached the subject of Marcus' biological father with Marcus, but Marcus had no desire to find out more. Meanwhile, Eric announced that he wanted to legally adopt Marcus, and Marcus began calling Eric "Dad." Justin and Marcus briefly met without knowing about their connection. Justin later spotted a photo of Donna and Marcus on Forrester Creations' web site and put the pieces together. Marcus did the same when he spied Donna and Justin in an innocent hug. Marcus welcomed Justin into his life, but he proceeded with becoming Eric's adoptive son.

Marcus was thrilled when Donna and Justin decided to marry. Marcus shared a "friends with benefits" relationship with Amber, but he was instantly smitten when he met Dayzee. Dayzee and Marcus dated and shared a few kisses, but she was hesitant to embark on a full-fledged romance while he was based in the Paris office. Marcus was relieved when Amber claimed Liam was the father of her unborn child, but when she gave birth to an African-American baby girl, it was apparent that Marcus was the dad. Marcus became a doting father to baby Rosie. Despite Amber's pressure to move in together as a family, Marcus was adamant that they were not a couple and that they'd share responsibility for their daughter. He moved back to L.A. permanently, and he and Dayzee consummated their relationship.