US Senator Amy Klobuchar will become the third 2020 Democratic presidential candidate in as many days to leave the race, following fellow moderate Pete Buttigieg's plan to endorse former vice president Joe Biden.
Ms Klobuchar of Minnesota will announce the suspension of her White House campaign in Dallas, Texas, where she will publicly back Mr Biden, a campaign aide said.
A reinvigorated Mr Biden, fresh off a resounding victory in Saturday's South Carolina primary, is heading into so-called Super Tuesday with fresh, high-profile endorsements.
Mr Biden is aiming for a strong showing against US senator Bernie Sanders, the national frontrunner and a democratic socialist from Vermont.
The Super Tuesday contests offer the biggest one-day haul of the 1991 delegates needed to win the party's nomination at its national convention in July.
About 1357 delegates, or nearly one-third of the total number, are up for grabs.
Billionaire former New York mayor Michael Bloomberg makes his first appearance on primary ballots in Super Tuesday states, where he has bet hundreds of millions of dollars of his own money to boost his campaign.
Five contenders remain for the nomination to take on Republican President Donald Trump in the November election, down from more than 20 earlier in the race.
Mr Buttigieg, the former mayor of South Bend, Indiana who entered the Democratic presidential race as a relative unknown, ended his White House bid on Sunday.
