Sen. Scott Brown burst onto the national scene nearly one year ago, helping to invigorate a moribund Republican Party and rejuvenating a Senate minority that had been unable to sustain a filibuster before his arrival as its 41st Member.

Boosted by victories in the New Jersey and Virginia gubernatorial races in 2009 and the yearlong fight over health care reform on Capitol Hill, the GOP was already rebounding after reaching a low point with the inauguration of President Barack Obama.

But the nature of Brown’s rise — winning a Jan. 19 special election to succeed the late liberal icon Edward Kennedy in heavily Democratic Massachusetts — was akin to a political earthquake that cracked the Democratic Party’s grip on power.

In an interview Jan. 7 to discuss his first year in office, Brown appeared simultaneously the humble, down-to-earth and previously unknown state legislator who arrived in Washington, D.C., last year; and a veteran Senator who is comfortable with his celebrity and cognizant of the power and influence he can wield.

“I’m blessed to be here. To be a United States Senator is certainly something I’m aware of and thoughtful and appreciative of,” Brown said, sitting in his office in the Russell Senate Office Building. “But it’s been a lot of fun. I’ve got to travel — Israel, Dubai, Jordan, Pakistan, Afghanistan. I’ve met with the president, the vice president a couple of times. I’ve met with all of our leaders on both sides of the aisle. I’m trying to get the country and the Congress moving together again. That’s what I’ve been doing.”

Brown’s autobiography, “Against All Odds: My Life of Hardship, Fast Breaks, and Second Chances,” is scheduled for release Feb. 21, according to Amazon.com. Few Senators have been treated with as much fanfare this early. Brown, who began his career in 1992 by winning the office of Wrentham, Mass., assessor, has proved to be the exception, and not just because of the circumstances surrounding his election.

He is telegenic and possesses natural charisma. He is a draw on the fundraising circuit, and is a commodity on Capitol Hill by virtue of being one of the few Northeastern Republicans in Congress and an occasional go-to guy for Democrats looking for GOP support on legislation.

Brown conceded that the media scrutiny he has faced has been a “little brighter” than anticipated. “I thought it would maybe subside, somewhat. But it’s always there at this constant pitch,” he said.

But he appears to have settled into a routine. He works long hours, sometimes sleeping on his office couch, and said he is using Kennedy as a model, in terms of his decision to focus on legislating and constituent service.

Brown even retained two Kennedy aides: Boston-based Constituent Services Specialist Emily Winterson and Mailroom Director Larry Bageant, who works in Washington, D.C.

Brown still refers to himself as a “Scott Brown Republican” who is conservative on fiscal, foreign policy and national defense issues. And he insists that bipartisanship should be a two-way street that, in his view, has been missing. “How many Democrats have voted for Republican initiatives? Check the voting records, it’s nonexistent,” the Senator said.

Brown fulfilled his campaign pledge to oppose Obama’s health care reform law, would vote to repeal it if given the chance, and has been a reliable GOP vote on major policy issues and key procedural votes. Still, he has crossed the aisle on some high-profile measures, including financial regulatory reform, the Strategic Arms Reduction Treaty and the repeal of the military’s “don’t ask, don’t tell” policy.

Brown said he uses five criteria to determine his position on legislation: Is it good for Massachusetts? Is it good for the country? Does it create jobs? Does the bill increase the deficit? Does it raise taxes? On those last two questions, the answer must be “no.”

“If it’s got three out of the five, then I’ll look at it. If it’s got none of the five, don’t even bother talking to me about it,” said Brown, who served in the Massachusetts House from 1998 to 2004, when he won a special election to the state Senate.

“Every single bill, whether it’s a Democrat bill or a Republican bill, I’ve looked at it with those five factors in mind,” he continued. “And, I also didn’t really care who was bringing it up, because as somebody who was not of Washington, Washington was clearly broken — they weren’t even talking. Then I got here and started voting across party lines and trying to get them to talk, to work together, to get our country moving again, because we’re in deep trouble. I think I’ve accomplished that to a point.”

Brown has been criticized in some conservative circles for his willingness to cross the aisle. But Sen. Jim DeMint (S.C.), a staunch conservative more than willing to publicly criticize fellow Republicans whom he believes have strayed, praised a colleague whose special election campaign he quietly supported, including financially.

“I think he’s obviously very popular in Massachusetts, I think he’s doing what the people of Massachusetts want. That’s what really matters right now,” DeMint said. “He’s doing a good job.”

Brown’s victory last year entitled him to the final two years of Kennedy’s ninth term. He is running for a full term in 2012 and figures to be a top Democratic target. His state is a Democratic bastion, and with presidential-year voter turnout, the challenge of winning as a Republican is multiplied. Money isn’t likely to be a problem: Brown estimates that he finished 2010 with $6 million in cash on hand.

National Republican Senatorial Committee Chairman John Cornyn (Texas) acknowledged the challenge ahead of Brown but argued that he begins the election cycle in perhaps as solid a political position as any of the GOP incumbents who are up.

“I think he’s well-prepared to go into this, what he knows is going to be a tough race,” Cornyn said. “But I’m optimistic he’ll hold the seat.”

Brown seemed amused with questions about his political viability and whether he can translate success in a lower-turnout special election to 2012. The Senator emphasized that his focus in 2011 is on legislating, even as he acknowledged preparations for his re-election bid.

“Am I raising money? Am I working hard? Of course, I never stop. I’m a Massachusetts Republican. I’m always the underdog,” Brown said. “Is there a surprise of some sort that I’m the underdog? I know that. I always have been.”