Williams averaged a career-high 15.5 points and hit 152 3-pointers in 80 games for Toronto, which will play Game 2 of its first-round series against the Wizards on Tuesday.
Williams is in his first season with the Raptors after stints with the Hawks and 76ers. Celtics guard Isaiah Thomas finished second in the balloting and Clippers guard Jamal Crawford was third.
Williams hit four of eight 3-pointers and went seven of seven from the free throw line.
The 29 points were the most for Williams since Dec. 28, when he scored 31.
Williams also added three steals and two assists to his totals. It was Williams sixth straight game scoring in double figures and seventh in his last nine.
Williams also dished out four assists and added two steals to his totals. It was Williams fourth straight game scoring in double figures and third consecutive with at least 18.
The Raptors never trailed in the game and completed a season sweep of the Pacers.
Williams shot eight-of-17 from the field, despite hitting just one of six 3-pointers. He scored 12 of his points in the fourth quarter, as the Raptors broke open a seven-point game and pulled away.
The Raptors next play against the Timberwolves on Wednesday.