The 38-year-old became the first openly g,a,y presidential candidate from a major party when he announced he was running for the Democratic nomination.
But despite a successful start, his campaign lost momentum in recent weeks.
His decision to drop out comes ahead of a key day on Tuesday in the Democratic race to take on Trump.
Fourteen states will vote on Super Tuesday, by the end of which staunch left-winger Bernie Sanders could have an unbeatable lead and be a step closer to the nomination.
His departure leaves six Democrats still in the race.
Speaking to supporters in his hometown of South Bend, Indiana, Mr Buttigieg stressed the values of truth he said his campaign had hoped to promote.
"And so we must recognise that at this point in the race, the best way to keep faith with those goals and ideals is to step aside and help bring our party and our nation together," he said. "So tonight I am making the difficult decision to suspend my campaign for the presidency."
He pledged he would do "everything in my power" to ensure a Democratic win in November's election.
Mr Buttigieg surprisingly, and narrowly, won the first event of the primary season, the caucuses in Iowa on 3 February. But he failed to repeat that success and win the delegates needed to make him the front- runner and later confirm his nomination. He finished a distant fourth in South Carolina on Saturday. // <\/s'+'cript>'); // --> //]]> From ICE
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