Charles Briscoe, Howard's agent, relayed the news to Shams Charania of Stadium and The Athletic.
Howard previously announced on Twitter that he was returning to the Los Angeles Lakers, but that tweet was quickly deleted, per David Aldridge of The Athletic.
Charania then reported that the big man was still considering his options before he ultimately landed with the Sixers.
Howard averaged 7.5 points, 7.3 rebounds and 1.1 blocks per game for the NBA champion Lakers last season. He should remain an asset for in the league, albeit one with limitations in today's NBA.
In Philadelphia, Howard should be the primary backup for All-Star big man Joel Embiid.
Howard is forced to hit the bench when teams play small, which notably happened when the Lakers played the Houston Rockets in the Western Conference semifinals. Howard also saw decreased playing time when the Heat ran with floor-stretching bigs like Kelly Olynyk.
But he's a clear asset when tasked with facing off against teams with more traditional bigs. Howard notably excelled against the Portland Trail Blazers in the first round, posting 9.5 points and 7.3 boards in the Lakers' four wins.
Howard, who turns 35 on Dec. 8, will be entering his 17th NBA season. He's made eight All-Star teams, eight All-NBA teams and five All-Defensive teams during his career.