In a race that was thought to be non-competitive until just weeks ago, Republican Scott Brown secured a massive upset victory over Democrat Martha Coakley in Massachusetts, winning Tuesday’s special election for the U.S. Senate seat previously held by liberal lion Ted Kennedy.

The outcome, which eliminates the Democratic caucus’ super-majority in the Senate, poses a significant risk to pending health care reform legislation.

Brown won by about 120,000 votes, or a 52 to 47 percent margin. According to polls, Coakley led by 31 points in November and by 17 at the beginning of January. But in the past week, Brown led in nearly every survey taken, and his five-point margin of victory was actually on the lower end of recent numbers.

His recent surge sparked national interest in the race, as President Barack Obama and former New York Mayor Rudy Giuliani went to Massachusetts to campaign for Coakley and Brown, respectively. On election day, despite inclement weather, Massachusetts Secretary of State William Galvin estimated that turnout may have been 50 percent.

Brown, a state senator, takes over a seat that has been held by the Kennedy family, except for a two-year interruption, since 1953; Ted Kennedy died in August after holding the seat for 47 years. Brown is the first Republican elected to the Senate from Massachusetts since Edward Burke in 1972.

“Tonight, the independent voice of Massachusetts has spoken,” Brown said after he was proclaimed the winner. “This Senate seat belongs to no one person, no one political party.”

He did express his admiration for Kennedy, an iconic figure in Massachusetts polics.

“Senator Ted Kennedy was a tireless and big-hearted public servant, and for most of my lifetime was a force like no other in this state,” Brown said. “There’s no replacing a man like that, but tonight I honor his memory, and I pledge my very best to be a worthy successor.”

Coakley, the attorney state general, did not take the loss lightly. “I am heartbroken at the result,” she said, conceding Tuesday night. She lost despite Obama’s 26-point victory just over a year ago and a gigantic gulf in voter registration in the state — Republicans account for only 12 percent of voters.

Coakley was labeled as an elitist and did little to dispel that notion. As the election wound down, she scoffed at the idea that she should shake hands with people, claiming that she was too busy and would instead rely on the support of local mayors and school boards.

One of her most widely publicized comments — that Boston Red Sox legend Curt Schilling, a Republican advocate, was a fan of the archrival New York Yankees — further enforced the idea that she was out of touch with her constituents. And in perhaps her biggest gaffe, Coakley, running a campaign with a heavy focus on law enforcement and security, claimed that Afghanistan was free of terrorists.

Brown, by contrast, played up an everyman image by driving his truck around the state, meeting with voters 66 times; Coakley made just 19 campaign stops. Coakley was not only unable to shake the superiority tag, but she was also unable to color Brown negatively. As a result, his working class persona prospered, and it was cemented by the time Coakley released a slew of desperate advertisements that tried, at the end, to craft the public’s view of Brown.

“There will be plenty of Wednesday-morning quarterbacking about what happened, what went right, what went wrong,” Coakley said. “We will be honest about the assessment of this race, and although I was very disappointed, I always respect the voters’ choice.”

The stunning outcome not only affects Massachusetts, but has significant national implications. Congress was expected to reconcile both the House and Senate versions of health care reform legislation early this year, with the Democrats’ 60-vote, filibuster-proof advantage acting as a restraint against any major changes from the bills passed in late 2009.

Ted Kennedy, a champion of reform throughout his career, refused to retire in August, despite brain cancer, because it would end the Democratic supermajority.

Brown, who is vocally opposed to the health care bill, will now break that stranglehold and put the entire process in doubt. Democratic leaders will now have to choose from a host of unpalatable options in proceeding: convincing their House majority to pass the Senate bill without changes, returning to deadlocked negotiations with Republican senators or bringing the bill to a vote it may not survive.

“One thing is clear: voters do not want the trillion-dollar health care bill that is being forced on the American people,” Brown said. “I will work in the Senate with Democrats and Republicans to reform health care in an open and honest way.”

Brown will take over for Paul Kirk, who holds the seat on an interim basis. Brown will have to run for reelection in 2012. He is expected to take his seat within the next couple of weeks.