The congresswoman also tweeted out a Warren-branded video, echoing Warren’s campaign rally cry and writing that “Big structural change can’t wait.”

“I have seen Ms. Warren in small church basements and in packed gymnasiums,” Pressley says in the video. “And she is consistent. She never loses sight of the people. You’ve all heard about the senator’s plans — but here’s the thing. Her plans are about power: who has it, who refuses to let it go, and who deserves more of it.”

Warren tweeted her thanks to Pressley, writing that “I'm proud to be fighting alongside you to put power in the hands of the people.”

Just a day earlier, Pressley told the Associated Press she’d been courted by a number of Democratic candidates, including Sanders and Biden but that for the time being she was focused on local elections.

Her endorsement comes as Warren continues to run in a tight primary with Biden and Sanders. After a lackluster beginning, Warren has risen steadily in the polls throughout the summer and into the fall overtaking Sanders for second place in most polls and surpassing Biden in others.

Pressley, the first black woman to represent the Massachusetts in Congress, hands Warren a surrogate within one of the Democratic Party’s most powerful constituencies, a demographic Biden maintains a solid lead with.

Pressley has often been grouped in with the group of freshman congresswomen of color colloquially known as “the squad" composed of Alexandria Ocasio-Cortez, Ilhan Omar and Rashida Tlaib. The group, which has sparred at times with Democratic leadership in the House but is extremely popular with the party's left wing, was pilloried over the summer in racist attacks by President Donald Trump in which he told the lawmakers to “go back” to the places “from which they came.”

The rest of the squad endorsed Sanders last month. But Pressley's split from the group is not entirely surprising.

While her path to Congress mirrored Ocasio-Cortez's in one respect — both women upset longtime Democratic congressmen — Pressley served on the Boston City Council for almost a decade before joining Congress as part of a diverse Democratic "blue wave" in last year's midterms. She was a delegate for Hillary Clinton in 2016, while Ocasio-Cortez has said Sanders' 2016 presidential run inspired her first foray into politics.

Pressley’s endorsement is likely to fuel speculation that the congresswoman could be in the running for Warren’s Senate seat should her White House bid be successful.

Pressley is far from the only member of Massachusetts' congressional delegation to endorse their home state senator — Ed Markey and Rep. Joe Kennedy, currently locked in a primary battle for Markey's Senate seat, and Katherine Clark, a member of House leadership, have also endorsed Warren.

Warren and Sanders, the two most prominent liberal candidates in the race, have been in a battle to secure endorsements from key progressive groups and figures on the left.

Last week, Rep. Katie Porter, a freshman from California and a rising star in the party, endorsed Warren. Also last month, Philadelphia Mayor Jim Kenney gave Warren her first endorsement from a big-city mayor.