"Three months ago, I entered the race for President to defeat Donald Trump. Today, I am leaving the race for the same reason: to defeat Donald Trump – because it is clear to me that staying in would make achieving that goal more difficult," Bloomberg said in a statement.
"I've always believed that defeating Donald Trump starts with uniting behind the candidate with the best shot to do it," the billionaire continued. "After yesterday's vote, it is clear that candidate is my friend and a great American, Joe Biden."
President Trump reacted by making fun of Bloomberg's campaign spending, which topped $450 million between November and March.
"I could have told him long ago that he didn't have what it takes, and he would have saved himself a billion dollars, the real cost," Trump tweeted Wednesday. "Now he will pour money into Sleepy Joe's campaign, hoping to save face. It won't work!"
Bloomberg won just one of the 15 Super Tuesday contests: American Samoa. He picked up 44 delegates Tuesday, far behind Biden's 399 and Bernie Sanders' 322, according to the Associated Press. Tuesday was the first time Bloomberg had been on the ballot, because he entered the race after the filing deadline for early voting states Iowa, New Hampshire, Nevada and South Carolina.
Biden thanked Bloomberg for the endorsement and for his "tireless work on everything from gun safety reform to climate change."
Trump dubbed Bloomberg the "biggest loser" of Super Tuesday.
FOX Business' Brittany De Lea contributed to this report.