Manchin, 72, who has served in the Senate since 2010 after previously serving as West Virginia’s governor, was unequivocal about his plans Thursday in an interview with Politico.
“I will, absolutely,” Manchin said when asked if he will support Biden.
In February, he said he might endorse President Trump for reelection – although he voted to remove him from office.
Manchin, who is one of the most conservative Democrats in the Senate, told Fox News last fall he wouldn’t support Sen. Bernie Sanders over Trump for president.
He told Politico his endorsement will come with a plan to help save West Virginia jobs.
“I will, [endorse] absolutely,” he told the outlet. “I’ve been working and talking to different people…You just can’t leave people behind that did the heavy lifting and that’s worked hard, whether it’s producing coal or producing energy for this country. They just need an opportunity to live their lives and have that opportunity.”
He said Biden “understands that.”
Manchin is one of many Democrats who have coalesced around Biden since his game-changing February win in South Carolina.
Wednesday, former rival Sen. Elizabeth Warren threw her support behind Biden and said she would be his vice president if asked.
Sanders dropped out of the race earlier this month and endorsed Biden this week.
Fox News’ Dom Calicchio contributed to this report