The Conservative premier offered Britain's deepest gratitude and good wishes to the 95-year-old as he stands down from public engagements.
"From his steadfast support for Her Majesty the Queen to his inspirational Duke of Edinburgh Awards and his patronage of hundreds of charities and good causes, his contribution to our United Kingdom, the Commonwealth and the wider world will be of huge benefit to us all for years to come," May said.
The Duke's retirement was revealed when the Queen's most senior aides were ordered to attend a special meeting at the palace in London – led by William Peel, the Lord Chamberlain. Staff were told that Philip would be retiring in September.
Labour leader Jeremy Corbyn said the monarch had dedicated his life to supporting The Queen and the UK. "His Duke of Edinburgh's Award scheme has inspired young people for more than 60 years in over 140 nations," the republican said. "We thank Prince Philip for his service to the country and wish him all the best in his well-earned retirement."
Ukip leader Paul Nuttall urged people to honour the Duke's public service. "For over 60 years he has been a dedicated public servant, and deserves our great thanks. Happy retirement Sir," he said.
But not all reactions to Philip's retirement news were flattering. Graham Smith, chief executive of campaign group Republic, said: "Philip himself admitted he had nothing to do with [the Duke of Edinburgh] Award scheme. Let's all stop the toadying."