Democracy for America, a progressive group that led the charge to draft Massachusetts Sen. Elizabeth Warren into the presidential race, said Thursday it would endorse Vermont Sen. Bernie Sanders for president.

This marks the first time that the 11-year-old organization, which grew out of Democrat Howard Dean’s 2004 campaign, has endorsed a candidate in the presidential primary. In the 2008 election, the group held a vote, but no candidate notched the requisite percentage of votes.

“Bernie...