Michael Bloomberg has ended his bid for the White House after a poor showing on Super Tuesday, the BBC reports.
“Three months ago, I entered the race for president to defeat Donald Trump. Today, I am leaving the race for the same reason,” he said.
Mr Bloomberg, a former mayor of New York City, has spent more than half a billion dollars in the race to become the Democratic Party’s nominee.
He said he would now support former Vice-President Joe Biden.
“I’ve always believed that defeating Donald Trump starts with uniting behind the candidate with the best shot to do it. After yesterday’s vote, it is clear that candidate is my friend and a great American, Joe Biden,” Mr Bloomberg said in his statement.
Out of the 14 states which voted on Tuesday, the billionaire only managed to win in American Samoa.
Joe Biden won nine of the states, a remarkable rebound for his campaign.
The former US vice-president overturned predictions to narrowly take the key state of Texas from his main challenger, Bernie Sanders.
However, Mr Sanders is projected to win California – the biggest prize of the night – as well as three other states.
They lead the race to face Republican President Donald Trump in November.