Booker ended his own presidential bid in January, pledging to do “everything in my power to elect the eventual Democratic nominee for president."
“The answer to hatred & division is to reignite our spirit of common purpose,” Booker tweeted.
Booker planned to appear with Biden in Detroit and Flint, Michigan later Monday, according to a Biden aide.
His decision follows recent Biden endorsements by several failed Democratic presidential candidates, including Sen. Kamala Harris of California and former Massachusetts Gov. Deval Patrick. Former Biden rivals Amy Klobuchar, Pete Buttigieg, Beto O'Rourke, Mike Bloomberg, Tim Ryan and John Delaney have also endorsed him.
Vermont Sen. Bernie Sanders has been endorsed by Marianne Williamson and Bill de Blasio.