The 6-foot-3 inch guard, who did not play college ball, was a second-round draft pick by the Warriors in 2005.
He increased his scoring to a career-high 16.5 points per game, which was the largest scoring increase in the NBA this season.
He also had per contest averages of 3.2 rebounds, 4.1 assists and nearly two steals in 77 games.
Ellis received 352 points -- including 47 first-place votes -- from a panel of 129 sportswriters and broadcasters throughout the United States and Canada.
The league noted that the voting was the closest since the 1990-91 season, when Scott Skiles of Orlando edged out Kevin Gamble of Boston by four votes.