Trump will meet members of the Royal Family and is expected to discuss climate change during talks with outgoing Prime Minister Theresa May.
Minutes before touching down, Trump criticised Mayor of London Sadiq Khan, with whom he has clashed in the past.
Protests are planned in several UK cities during the visit, including London, Manchester, Belfast, and Birmingham.
Trump was greeted by US Ambassador to the UK Woody Johnson and Foreign Secretary Jeremy Hunt.
Tory leadership candidate Hunt, who has spoken about the importance of the UK’s relationship with the US, said Mr Trump mentioned to him “some of his very strong views about the Mayor of London” which he had also tweeted.
Trump’s tweet accused Khan of doing a “terrible job” as mayor, adding: “[He] has been foolishly “nasty” to the visiting President of the United States, by far the most important ally of the United Kingdom. He is a stone-cold loser who should focus on crime in London, not me.”
A spokesman for Khan said “childish insults” should be beneath the US President, adding: “Sadiq is representing the progressive values of London and our country, warning that Donald Trump is the most terrible example of a growing far-right threat around the globe.”
Although Trump has spoken of his admiration for Mrs May, there is expected to be differences of opinion during their talks, which begin tomorrow Tuesday.
The prime minister will raise the issue of climate change, with a government spokesman again saying on Monday the UK was “disappointed by the US decision to withdraw from the Paris Agreement in 2017”.
The two leaders are also expected to discuss Huawei. The US has blacklisted the Chinese firm for security reasons, while the UK may allow it to supply “non-core” components for its 5G network.