Prime Minister Matteo Renzi, who had supported Democratic candidate Hilary Clinton during the presidential race, congratulated Trump.
"I wish him good luck in his work. The Italian-American friendship is solid," Renzi said.
"Italy will continue with friendship and collaboration with the USA," Foreign Minister Paolo Gentiloni confirmed in a radio interview. "These things don't change, just as our aversion to protectionism does not change."
However, Gentiloni admitted that "a lot of things will change" as a result of the election result. He had earlier said that a Trump victory would have "enormous consequences" and that he did not expect the businessman to win.
Laura Boldrini, President of the Chamber of Deputies and a prominent campaigner for women's rights, said: "Today I had thought I'd be commenting on a different result. Huge surprise but also respect for the choice of the electorate.
"Democracy is evident in the capacity for surprise, as happened eight years ago with Obama and today with Trump. Hillary Clinton was defeated not because she was a woman, but because she's seen as an expression of the establishment."
However, there were some politicians in Italy who greeted the surprise announcement positively.
The leader of the far-right Northern League party, Matteo Salvini, shared a gleeful Tweet, featuring a picture of him and Trump, the slogan 'Good morning!' and the hashtag '#GoDonaldGo'. He later described the Republican's win as "a blow to globalization".