Keane - Galaxy's designated player - beat fellow strikers Obafemi Martins (Seattle Sounders), Lee Nguyen (New England Revolution) and Bradley Wright-Phillips (New York Red Bulls) to the award that is voted on by media, MLS players and the division's club management.
The 34-year-old Republic of Ireland international has been in dazzling form for the Galaxy, who will face the Revolution in Sunday's MLS Cup final at StubHub Center in Los Angeles, scoring a career-high 19 MLS goals and 14 assists as Bruce Arena's men finished second in the Western Conference.
Keane, who move to Los Angeles in 2011, is the third Galaxy player to be named MVP of the competition, following in the footsteps of Carlos Ruiz (2002) and Landon Donovan (2009).
Meanwhile, DC United's Bill Hamid was named MLS Goalkeeper of the Year ahead of Real Salt Lake counterpart Nick Rimando.
United conceded the joint lowest number of goals, 37, as they topped the standings in the Eastern Conference.
Vancouver Whitecaps midfielder Pedro Morales took out the Newcomer of the Year award.
Get the best features, fun and footballing frolics straight to your inbox every week.