The actor was involved in a controversial lawsuit against the University of Texas at Austin, Fawcett's alma mater.
O'Neal claimed Warhol painted two multi-million dollar images of the 1980s icon: one for O'Neal, one for Farrah. The college sued O'Neal in 2011, claiming Fawcett owned both portraits and that she left all of her artwork to them in a living trust.
One portrait was on display at the University of Texas Blanton Museum of Art, while the coveted piece was on display in O'Neal beachside home. The university wanted to obtain the second one from O'Neal to display next to the one they already owned.
During the three-week trial, O'Neal testified that he took the portrait from Fawcett's condominium about a week after she died, but claimed the second painting was always his.
O'Neal said that he arranged for Fawcett to pose for Warhol, and in return, Warhol made the second silkscreen portrait for him.
University lawyers said Fawcett repeatedly claimed she was the portrait's owner. O'Neal's lawyer, Marty Singer, said the actress meant to give the university art she created, and not art she purchased.
The case dissected Fawcett's final wishes and her relationship with O'Neal who was Fawcett's longtime companion. O'Neal and Fawcett were never married, but lived together from 1980 through 1988. O'Neal said they broke up at that point when Fawcett found him in bed with a 25-year-old woman.
O'Neal says he and Fawcett moved back in together in 2001 when he was diagnosed with cancer and stayed a couple until she died from cancer in 2009.
University lawyers attempted to discredit O'Neal's ownership claims with footage from Fawcett's reality show and a "20/20" television segment documenting the portraits' creation.
The portrait has been a cherished possession for O'Neal, who told jurors it is one of the strongest reminders of his nearly three-decade off-and-on romance with Fawcett.
O'Neal told the court he was not planning to sell the portrait, and that it would be passed on to Redmond O'Neal, the couple's only child together.
After Thursday's verdict, Redmond and Patrick O'Neal spoke about their father's big victory in court.
"We're just absolutely over the moon, we're thrilled because the truth came out," they said. "In the end, they came here and said so many awful, terrible lies and it was so hard to sit here for so long and it's just an awesome, awesome feeling. It's a great Christmas gift, you know."
Ryan O'Neal was absent for the verdict Thursday. His attorney said his absence was due to a surgical procedure.
The University of Texas is reportedly considering to file an appeal.
The Associated Press contributed to this report.