During his stay the president is expected to give his views on Britain's forthcoming EU referendum, and advise voters to remain in the union, BBC reported.
He and First Lady Michelle Obama are due to have lunch with the Queen at Windsor on Friday, and dinner with the Duke and Duchess of Cambridge.
Obama will also speak at a news conference with Prime Minister David Cameron.
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His Britain stay is part of a tour which also includes a visit to Germany and Saudi Arabia - from where he has just left after having discussions with King Salman on issues including Iran, Syria, Yemen and the fight against so-called Islamic State militants.
Obama arrived at Stansted Airport and was greeted by the the Lord Lieutenant of Essex, John Petre, and the US Ambassador to Britain, Matthew Barzun.
The Obamas previously met the Queen, Prince Philip and the Duke and Duchess of Cambridge during their state visit in 2011.