"Never before a president of my country had been invited to pay a state visit to the UK," Santos was quoted as saying by Prensa Latina.
Santos was welcomed by the Queen and the Duke of Edinburgh at the Royal Pavilion on Horse Guards Parade with the prime minister, the foreign secretary and the home secretary in attendance.
According to a statement published on the UK government website, on Wednesday Santos will meet with Prime Minister Theresa May and Foreign Secretary Boris Johnson, as well as attend a number of events at various schools and museums.
On Thursday, Santos, who has been leading Colombia’s peace process, will travel to Belfast to learn about Northern Ireland’s experience of peace-building.
The Colombian leader will also hold meetings with the Prince of Wales, the mayor of London Financial District and parliament officials.
Such topics as bilateral cooperation, education, environmental issues, as well as trade and business opportunities for UK exporters and investors in various spheres are expected to be discussed.
Colombia was mired in a half-century war between the Revolutionary Armed Forces of Colombia (FARC) and the Colombian government, which has claimed lives of a quarter of a million people. The two parties began peace talks in November 2012 and signed a historic ceasefire agreement in Cuba on August 24. The sides signed a peace deal in late September.
On October 2, Colombia's National Election Council said the peace agreement between the government and FARC rebel movement, signed in September, failed to garner the support of the majority of Colombian voters at a referendum, with 50.22 percent opposed to the deal and 49.78 in favor.
On October 4, Santos announced the start of a new national peace dialogue in the country with the FARC. On October 7, he was awarded the 2016 Nobel Peace Prize for his efforts to end decades-long war between the country's government and the FARC guerrillas.