Beckham, the former English captain who also starred for Manchester United, will join the Galaxy after his contract with Real Madrid expires on June 30. Los Angeles opens its season April 8 in Houston.
"I am proud to have played for two of the biggest clubs in football and I look forward to the new challenge of growing the world's most popular game in a country that is as passionate about its sport as my own," he said in a statement released Thursday.
The move was announced following the end of talks on extending the 31-year-old English midfielder's contract with the Spanish club. MLS recently changed its rules on salary caps, clearing the way for Beckham to sign a lucrative deal. British news reports put the Galaxy deal at $250 million.
"This week, Real Madrid asked me to make a decision regarding my future and the offer to extend my contract by a further two seasons," Beckham said in the statement. "After discussing several options with my family and advisers to either stay here at Madrid or join other major British and European clubs, I have decided to join the Los Angeles Galaxy and play in the MLS from August this year."
Beckham has soccer academies in London and Los Angeles. His wife Victoria, a former Spice Girl, was recently photographed househunting in Los Angeles.
In Europe, what they call "football" is king, and Beckham's as close to royalty as you can get, CBS News correspondent Mark Phillips reports. But in mainstream America, he's at best 'what's her name's husband.'"
"David Beckham will have a greater impact on soccer in America than any athlete has ever had on a sport globally," said Timothy J. Leiweke, president & CEO of Anschutz Entertainment Group, which owns the Galaxy. "David is truly the only individual that can build the bridge between soccer in America and the rest of the world."
Beckham joined Real Madrid in 2003 after a hugely successful run with Manchester United, where he won six league titles, two FA Cups and the Champions League title. But Beckham did not win a single major trophy with the Spanish club, and his spell coincided with Madrid's worst slump since the early 1950s.
Real Madrid has had six different coaches and three club presidents during Beckham's stay, but the club has made a fortune — in part because of the star's position as a cultural icon for soccer fans and non-fans alike, including men, women and children of different ethnic and racial groups.
His marketability was emphasized by the hit movie "Bend It Like Beckham," even as his skills deteriorated with age.
Beckham's contract included a clause in which half his image rights would go to Real Madrid. That helped earn the club millions, allowing the Spanish team to overtake Manchester United as the biggest earner in world soccer.
Beckham led England to the quarterfinals of the World Cup last summer, scoring from a free kick in the second round to beat Ecuador 1-0. But he was taken off the field early in the second half against Portugal with ankle and Achilles tendon injuries, and then watched as his team was eliminated in a penalty shootout.
A day after the game, Beckham stepped down as captain of the team — a post he had held for 58 of his 94 international appearances. Then, on Aug. 11, England coach Steve McClaren dropped Beckham from the team altogether, signaling the end of his international career.