Leading up to the 1995 NBA Draft, O'Bannon hoped to be drafted by a team on the west coast. Selected ninth overall by the New Jersey Nets, he signed a three-year, $3.9 million contract. However, he became homesick. In his two professional seasons, he was unable to find a place in the NBA, being too lean to play down low and not quick enough with his rebuilt knees to guard the perimeter. His knee also started to break down. He averaged 6.2 and 4.2 points per game respectively with the Nets and was traded to the Dallas Mavericks later in his second and final NBA season, where he had even less of an impact. In September 1997 he was traded along with Derek Harper to the Orlando Magic and released. "It wasn't injury, it was confidence," O'Bannon said about his NBA career. "I missed shots, got pulled from games, it affected my defense, and I lost all my confidence." Former Nets teammate Armon Gilliam said, "He's a guy who didn't find his niche in the NBA. He wasn't in the right situation to grow and develop. He never got the opportunity to prove what he could do."
As of 2009, O'Bannon was employed as a marketing director for a Las Vegas auto dealership. In 2006, while employed as a salesman at the dealership, O'Bannon told the Los Angeles Times, "People see me and remember me and I'm proud to tell them — 'No, I don't play. No, I don't coach. Yes, I sell cars.'"
O'Bannon is the lead plaintiff in O'Bannon v. NCAA, an antitrustclass action lawsuit filed against the National Collegiate Athletic Association (NCAA) on behalf of its Division I football and men's basketball players over the organization's use for commercial purposes of the images of its former student athletes. The suit argued that upon graduation, a former student athlete should become entitled to financial compensation for future commercial uses of his or her image by the NCAA. In January 2011, Oscar Robertson, considered one of the greatest basketball players of all-time, joined O'Bannon in the class action suit.
O'Bannon attended UNLV to continue earning his bachelor's degree. In the summer of 2011, O'Bannon returned to UCLA to complete his studies, and he graduated in the fall that year with a degree in History from UCLA.
O'Bannon is the older brother of Charles, who played with him at UCLA and went on to play for the Detroit Pistons.