Harvard Law School professor Elizabeth Warren handily defeated U.S. Senator Scott Brown Tuesday night, becoming the first woman elected to the United States Senate in Massachusetts history and reclaiming for her party the seat held for decades by Democratic legend Edward M. Kennedy ’54-’56.

Though early in the night it looked as if the margin of victory might be narrow, Warren ultimately beat Brown by 10 points, 54 percent to 46 percent, riding the wave of Democratic support in Massachusetts that also led President Barack Obama to a large margin of victory in the state.

Addressing a crowd of cheering supporters at the Fairmont Copley Plaza in Back Bay after her victory Tuesday night, Warren stressed campaign trail promises to champion the struggling middle class and be a liberal bastion for the people of Massachusetts.

“For every family that has been chipped at, squeezed, and hammered, we’re going to fight for a level playing field,” Warren said. “To all the small business owners tired of a system rigged against them, we’re going to hold the big guys accountable.”

“I won’t just be your senator, I will be your champion,” she concluded.

Warren’s victory Tuesday night cemented Democratic control of the Senate. She has pledged to work to raise taxes on the nation’s top earners and cut military spending in order to reinvest in infrastructure, jobs, and education.

“This Warren victory is just one of many victories that the Democrats are rolling up,” Kennedy School professor Richard D. Parker said.

At press time, Democrats had won 22 of 33 Senate seats on the ballot Tuesday according to New York Times projections. The Republicans were projected to win the House and at press time had won seven Senate seats.

Though her victory was a reaffirmation of the Bay State’s traditionally Democratic politics, Warren expressed her appreciation for Brown’s efforts at bipartisanship, saying she will work across the aisle in Washington.

“I also want to say tonight to Senator Brown’s supporters, the message you sent was clear. We need more leaders in Washington who are willing to break the partisan gridlock and work regardless of party,” Warren said. “I know I didn’t earn your vote, but I promise to work to win your support.”

Political experts have called Warren’s win a “return to normalcy” for left-leaning Massachusetts. The closeness of the race over the last year speaks to Brown’s popularity and moderate politics, but Tuesday night’s result makes his 2010 special election victory look more like an aberration than indicative of a new political norm.

After a hard-fought and at times bitter race, Brown graciously conceded the race to Warren in front of his downcast supporters at the Park Plaza Hotel, just blocks away from Warren’s celebration unfolding at the Fairmont.

“She has received the high honor of holding the people’s seat,” Brown said. “May she bring that senate office great credit.”

Hinting that another run might still be in his future, Brown said “defeat is only temporary” and reminded supporters that politics is about responding to the will of the people. He said he leaves office as dedicated to independent politics as when he entered it.

“As you know, it’s been two statewide campaigns in three years.... What matters even more is what we achieved in between these two elections.” Brown said. “I kept my promise to you to be that independent voice to Massachusetts, and I have never ever, ever, regretted any decision I made for you.”

The same combination of moderate political stances and personal appeal that led to Brown’s victory in 2010 often made it seem that he could pull off reelection. Warren struggled to gain political footing early in the campaign and even as Massachusetts enthusiastically supported the president, his former adviser initially failed to win over the independents and conservative Democrats who helped elect Brown in 2010.

Ultimately those groups sufficiently coalesced around Warren as she tapped the combined benefits of near-record voter turnout and an unparalleled grassroots ground game.

Though not all the votes had been tabulated at press time, voter turnout in Massachusetts topped three million, approaching a record high.

In the Democratic strongholds of Boston and Cambridge, Warren won 74 percent and 85 percent, respectively. But she was also able to cut into Brown’s margins along the North and South shores, where he won convincingly in 2010.

Warren campaign volunteers knocked on over 200,000 doors and made 600,000 phone calls the weekend before Election Day, according to the campaign’s press secretary Alethea Harney. They expected to have deployed some 20,000 volunteers by the time polls closed Tuesday.

“This was a campaign that broke records, raising more money from small donors than any Senate campaign before it, knocking on more doors,” Warren said. “And let me be clear, I didn’t build that, you built that.”

Both Brown and Warren were boosted throughout the year-long race by a great deal of out-of-state financial and organizational support. The match-up proved to be the most expensive and hotly contested Congressional race in the country, costing more than $68 million and prompting a parade of national political figures to weigh in on both sides.

Warren, 63, began her career at the University of Houston Law Center in the late 1970s and spent more than three decades climbing the academic ladder as a legal expert focusing on consumer finance. She gained national prominence as the chief regulator for the government’s TARP bailout program in 2008 and then as the intellectual founder of the Consumer Financial Protection Bureau.

Warren has been the Leo Gottleib professor of Law at Harvard since 1995 and her husband, Bruce H. Mann, is a professor at the Law School. Warren, who has been on leave since declaring her candidacy for Senate last fall, will vacate her professorship officially at the end of the semester.

—Staff writer Nicholas P. Fandos can be reached at nicholasfandos@college.harvard.edu.