The owners voted 30-0 -- during a 10-day balloting period that began at the Jan. 12 quarterly owners meetings -- to extend Selig's contract through the 2014 season.
Selig will be 80 when his term expires Dec. 31, 2014.
"It is a great honor to have the unanimous support of the clubs," he said. "I am thankful for their confidence, and I look forward to representing and continuing the remarkable growth of this great game in the years ahead."
Should the former Milwaukee Brewers owner complete a full term, he will have served as baseball commissioner for 22 years -- longer than any commissioner in history except the first one, Kennesaw Mountain Landis, who held the post for 24 years before his death in 1944.