O'Neal reiterated what he revealed in a video posted to Twitter two days ago, saying that after 19 years in the NBA, his playing days are over.
On his Twitter account, O'Neal simply wrote, "im retiring," with a link to a 16-second video in which he says, "We did it. Nineteen years, baby. Thank you very much. That's why I'm telling you first. I'm about to retire. Love you. Talk to you soon."
O'Neal is a 15-time All-Star who won the league Most Valuable Player award in 2000 and won four championships, three with the Los Angeles Lakers, one with the Miami Heat.
The veteran struggled to get on the court last season because of injuries. He played just 37 games this year, the first of a two-year deal with the Boston Celtics. The 39-year-old made just three brief appearances after Feb. 1.
O'Neal signed with the Lakers in 1996 and had his greatest success there, winning three titles alongside Kobe Bryant and coach Phil Jackson.
However, O'Neal was traded to the Heat in the summer of 2004 amid tension between O'Neal and Bryant after a loss to the Detroit Pistons in the finals.
O'Neal spent 3 1/2 years in Miami before moving to Phoenix and then Cleveland and finally Boston.
At each stop, he endeared himself to the fans and his new teammates with his effervescent smile and playful attitude, including the habit of adopting a new nickname that he felt embodied his role with his new team. In Phoenix he was the "Big Shaqtus"; in Boston, the "Big Shamroq."
O'Neal retires fifth all-time with 28,596 points, 12th with 13,099 rebounds and a .582 field goal percentage that is second only to Artis Gilmore among players with more than 2,000 baskets. His ability to shoot a free throw was perhaps his biggest shortcoming. His percentage stands at .527.
The Associated Press contributed to this report.