Justin Barber was the son of Wesley Barber and Valerie Lowell, and was related to the Barbers of Genoa City, Wisconsin. An executive at Spencer Publications, Bill Spencer, Jr. brought Justin out from New York to work alongside him in Spencer's home office in Los Angeles. Justin's main assignment was to aid in Bill's takeover of Forrester Creations.
Justin attended the same high school as Donna Logan in Los Angeles' San Fernando Valley. Justin and Donna had dated, but Donna had suddenly broken things off and headed for Europe, leaving Justin unaware of Donna's fate. Upon his return to Los Angeles, Justin ran into Donna, who was circumspect about the years they were out of touch. When Marcus Walton interrupted the conversation, Donna ushered Marcus out. Justin's curiosity was piqued, so he researched the Forresters on-line and discovered that Donna had just reconnected with Marcus, the son she had given up for adoption. Before long, Justin and Marcus realized they were father and son, and decided to get to know one another, even as Marcus had just been legally adopted by Donna's husband, Eric Forrester.
After Bill completed his takeover of Forrester, Justin gave Donna, who was now vice president of Forrester, a chance to host his fashion talk show, The Catwalk. Donna's nemesis, Pam Douglas, horned in on the proceedings and ended up co-hosting with Donna. Justin felt the frenemies were good for ratings, and enjoyed the chance to be closer to Donna, which annoyed Eric. Justin also found himself a confidant to the usually secretive Bill. Donna's marriage felt apart after Donna Logan's Alzheimer's-stricken mother, Beth Logan, drowned in Eric's swimming pool. Justin was instrumental in convincing Donna to ask for half of Eric's shares in Forrester (12.5%), which Donna then sold to Bill.
Young Steffy Forrester had set up a seduction to trick Bill into returning control of Forrester, so when Steffy was putting together a tribute video to Donna's sister, Brooke Logan, Justin took action. Justin got the video off of Steffy's laptop, which was being fixed by Spencer computer tech Liam Cooper (who later turned out to be Bill's son). Liam had accidentally recorded Steffy's conversation about Brooke's "mistaken identity sex" with her daughter's boyfriend, so Justin added the audio to Steffy's video, and Brooke's indiscretion was leaked to the world. Bill was furious with Justin since Brooke was the sister of Bill's wife, Katie Logan.
Justin continued working at Bill's right-hand man, and spent more time with Donna and Marcus as a family. Justin and Donna decided to revive their former romance, and Donna proposed to Justin. Donna and Justin married in Bill's beach house in Malibu with Logans and Spencers in attendance, as well as Olivia Barber Winters, Justin's cousin who was visiting from Genoa City. Justin asked if Marcus would change his last name to Barber, and Marcus said he would consider it, although he never confirmed one way or the other. Justin later leaked the news of Steffy's engagement to Liam at the behest of Bill, who wanted Liam's ex-fiancee, Hope Logan, to see it.
When Katie was recovering from a heart attack, Justin encountered Katie's specialist, Dr. Malaika Maponya. Justin and Malaika discussed how they had known each other when they lived in South Africa. Justin asked Malaika to stay for a few days, but Malaika thought it wasn't a good idea since Justin was now married. Malaika gave Justin a kiss goodbye on the cheek, but Justin pulled Malaika in for a full kiss. Donna walked in moments later and thanked Malaika for caring for Katie. When Malaika left, Justin seemed distant, which Donna didn't notice.
Months later, Justin and Donna took Brooke and Katie to lunch and announced they were getting a divorce (though there was no mention of whether Malaika had played a part in it). Donna admitted that she and Justin had reunited too fast, and basically gotten married so Marcus could have his parents together. Justin and Donna realized they were better friends than lovers, and went their separate ways.
As Liam's divorce from Steffy became final and Liam planned to marry Hope in Italy, Bill recruited Justin to help him disrupt the wedding by finding Hope's father, Deacon Sharpe, whom Hope hadn't seen since she was a baby. Justin accidentally "pocket dialed" Marcus on his cell phone while Justin and Bill were discussing the scheme, and Marcus overheard. Marcus confronted Justin about it, but Justin nervously refused to divulge anything, and the Forresters travelled to Italy for Hope and Liam's wedding. Months later, Marcus finally told his wife, Dayzee Leigh, about what he heard. Hope bashed through Bill's window with a golf club after finding out from Dayzee what Bill had done.
Eventually, Liam remarried Steffy, which Bill approved of. Justin ribbed Bill about Liam having made the decision on his own without Bill's usual undue influence. Justin also met Carter Walton, Marcus' adoptive brother. Off-screen, Justin helped Bill dig up dirt on the wrongly convicted Maya Avant for the purpose of getting Maya away from Rick Forrester, who was dating Bill's niece, Caroline Spencer.
When news broke that Bill had slept with Brooke, and that Brooke had miscarried Bill's baby, Katie filed for divorce, and Justin served as Bill's attorney. Justin approved Katie's divorce settlement, in which she only asked for the house and 1% of Spencer Publications. What he didn't realize is that the move left Bill with a 49% share of the company while Karen Spencer, Bill's half-sister and absentee co-owner, retained her 50% and was now Spencer's majority stockholder. Karen appointed Katie CEO, and Katie's first order of business was to fire Bill and have him removed by security guards! Justin was forced to admit that the settlement papers were legitimate.
Months later, Bill ended his relationship with Brooke and returned to Katie, so Justin presented her with papers that would return control of Spencer to Bill and allow Bill joint custody of his son, Will. Katie didn't know that Justin was in on Bill's plan to trick Katie into signing, and Justin didn't know until he opened the envelope that Brooke, who had discovered Bill's deception, had replaced Bill's papers with a pile of leaves, rendering the power transfer null and void. When Bill remained despondent over losing Brooke, who went back to her on-again-off-again true love, Ridge Forrester, Justin uncovered photos of Ridge with his arm around a man at a gay pride parade and gave them to Bill to show Brooke, hoping to clear the way for Bill and Brooke to reunite.
When Bill finally convinced Brooke to marry him in the Middle East, he brought Justin with him to make sure nothing went wrong. Ridge flew to Abu Dhabi to stop Brooke's wedding to Bill, providing proof that Bill had slept with his ex-girlfriend, Quinn Fuller. Ridge dragged Brooke away and into a waiting helicopter that was actually piloted by Justin. Bill ordered Justin to “cool him off,” so Justin banked the chopper, which sent Ridge plunging into the Persian Gulf. When Ridge went missing, Bill insisted to Justin that he only wanted to teach Ridge a lesson, not hurt him; Justin retorted that he was only following Bill's orders, and recalled that Ridge might have seen the Spencer logo on his jacket before falling. Justin and Bill were relieved when Ridge turned up alive, but more so because Ridge had suffered a concussion that had impaired his memory.