According to Reuters, Beckham has signed a deal which will likely take him to the end of his professional playing career, having previously joined Real Madrid for £25m in 2003.
Beckham said: "This week Real asked me to make a decision regarding my future and they offered to extend my contract for a further two seasons. After considering several options to stay in Madrid or join other major British and European teams, I have decided to join LA Galaxy."
The 31-year-old was first choice on the Real Madrid team sheet until Italian coach Fabio Capello took charge of the club in June last year.
He will be the most famous player to sign up for Major League Soccer since it began in 1996. Previous footballers to play in the US, in what was the North American Soccer League, include Pele, who played for the New York Cosmos, and Bobby Moore, who played for San Antonio Thunder.
The deal is reported to be one of the biggest in global sport with Beckham set to earn more than $250m over the duration of his contract.
During his time with Real Madrid Beckham helped it topple Manchester United as the world's richest football club and biggest brand and signed a string pf personal sponsorship contracts including the likes of Gillette and Pepsi.
He has only started five of Real's 16 league games this season and was known to be frustrated with his lack of opportunities in the first team. The midfielder was dropped from the England squad indefinitely after he renounced his captaincy following England's disappointing World Cup performance.
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