The influential former leader was one of the last Democratic heavy hitters to offer his endorsement, with Harris having already received the backing of President Joe Biden on Sunday to take his place on the ballot.
Obama’s backing will add to the growing momentum behind Harris’ campaign, which has enjoyed a groundswell of support since she announced her 11th-hour candidacy.
Harris, 59 years old, jumped into the election after weeks of turmoil over 81-year-old Biden, who bowed out after a dismal debate performance against Trump accelerated concerns over his mental capacity and persistently low polling numbers.
The country’s first woman vice president — who is seeking to make history again in November — launched a blistering attack on Trump and his extremist Republicans as she addressed teachers on Thursday.
The momentum appeared to catch Trump off guard, with the bombastic Republican refusing to schedule a debate with Harris, saying Thursday night it would be inappropriate until she was officially named the Democratic nominee.