The Sixers beat the Indiana Pacers 105-95 in Wednesday's regular-season finale but missed the playoffs by four games. The team has qualified for the playoffs the previous two seasons under Collins.
Collins, 61, was the coach at Philadelphia for three seasons, building a 110-120 record. He previously coached at the Chicago Bulls, Detroit Pistons and Washington Wizards and has an 11-season record of 442-407.
The only seasons his teams failed to advance to the playoffs were 1997-98, when he was fired by the Pistons 45 games into the season; both of his seasons in Washington; and this year.
Collins said Thursday that he decided late last year that this would be his final season as an NBA coach but is expected to remain with the Sixers as an adviser. Team officials stressed it was Collins' decision to step down.
Collins played in the NBA from 1973-81 -- all with Philadelphia -- earning four All-Star team selections.