Leonard received 547 points and 84 first-place votes from the voting panel of 130 sportswriters and broadcasters.
Golden State Warriors power forward Draymond Green (421 points, 44 first-place votes) finished second for the second straight season. He was followed by Miami Heat center Hassan Whiteside (83 points, two first-place votes) in third.
Leonard is a defensive leader for the Spurs, who allowed the fewest points per game during the regular season, giving up three points fewer per contest than the Utah Jazz in second. The Spurs had a defensive rating of 94.9 with Leonard on the court and 99.2 when he wasn't, according to NBA.com/Stats.
Individually, Leonard tallied 1.8 steals and 1.0 blocks per game. He ranked fifth in the NBA in Defensive Real Plus-Minus as the only non-power forward or center in the top 25.
Leonard was named to his first All-Star team this season.
Leonard is just the second perimeter player in NBA history to win the award in consecutive seasons, joining Milwaukee's Sidney Moncrief in 1982-83 and 1983-84, the first two seasons the award was given. Leonard was the first non-big man to win the award since Ron Artest in 2003-04 when he earned the honor last season.
Information from ESPN's Marc Stein and Kevin Pelton and The Associated Press contributed to this report.