Michael Bloomberg will endorse Hillary Clinton in a speech at the upcoming Democratic National Convention.
A spokesman for Bloomberg says he will make the endorsement speech Wednesday night.
The billionaire media mogul was considering making a presidential run as a third-party candidate but opted out amid concerns it might help Trump win the election.
Bloomberg has previously been critical of Trump, in particular his views on immigration and international trade.
He was a Democrat before switching his party affiliation to Republican prior to his successful 2001 run for mayor.
He later became an independent.