BOSTON Elizabeth Warren, a darling of the left, won a hard-fought race for the U.S. Senate in Massachusetts on Tuesday, according to network projections, recapturing for the Democrats the seat held for almost half a century by Edward M. Kennedy.

The networks began calling the race for Warren shortly before 10 p.m., first CBS and then CNN and NBC. Wild whoops went up in the hotel ballroom here where Warren was holding her victory party.

The Senate seat had slipped into Republican hands when Brown, a state legislator, won it in a special election in 2010 after Kennedy’s death. Taking it back was a Democratic priority.

Warren, 63, a professor at Harvard Law School, will become the first woman to win a Senate seat in Massachusetts. Her victory was fueled by a forceful appeal to female voters, who supported her in lopsided numbers, while men overwhelmingly backed Brown.

She cast herself as a fighter for the middle class and a champion of women’s causes, particularly equal pay for equal work, health insurance coverage for birth control and abortion rights.

It was a message that resonated with Elizabeth Lear, 46, a book reviewer in Waltham, who said she voted for Warren because “she cares about the financial concerns of everybody and most importantly about women’s reproductive rights, the freedom to choose.”

And, Lear added, “I feel she’s pretty scrappy and I really like that about her.”

Brown cast Warren as a partisan and inflexible ideologue who would march in lockstep with the Democratic Party.

The combined spending on the race totaled more than $68 million, making it the most expensive Senate race in the country in this election cycle and one of the most expensive ever. With the help of progressive groups that bolstered her candidacy early, Warren raised a stunning $39 million, which put her among the top five most successful Senate fundraisers of all time. The money was all the more remarkable considering that Warren was a first-time, and untested, candidate.

“We raised money from more donors than any Senate campaign in the history of the United States,” Warren said in a statement about an hour after the polls closed Tuesday. She added: “We knocked on more doors and made more phone calls than any candidate in the history of the Commonwealth of Massachusetts.”