CBS News reported on its Web site Thursday the announcement will come Friday morning in Warren, Mich. The former political opponents will campaign together through Michigan a day before the state's Democratic caucus on Saturday.
Nearly all of the Democratic campaigns have sought the backing of Gephardt, the influential former House minority leader.
"There are two reasons Gephardt's backing is important to Kerry," Donna Brazile, Al Gore's campaign manager in 2000, told CBS. "Gephardt has a lot of credibility with labor. The states to come are labor intensive. Dick Gephardt has a lot of institutional support. He left the campaign on good graces. Dick Gephardt could conceivably be a potential VP candidate."
Kerry picked up endorsements Thursday from former U.S. Sen. George Mitchell of Maine and Maine Gov. John Baldacci. And on Wednesday, the Massachusetts senator was endorsed by the 1.3 million-member American Federation of Teachers.