Ennis reportedly declined more lucrative offers from multiple teams.
The 29-year-old has played for six teams in five seasons since entering the league in 2014. The 76ers acquired him from the Houston Rockets ahead of February's trade deadline and he played a crucial reserve role in the playoffs.
Ennis remains a strong perimeter defender who has flashed some potential as a 3-point shooter.
He averaged 6.7 points and 3.1 rebounds across 58 games with Houston and Philadelphia last season.