PORTSMOUTH, N.H. — Scott Brown, who rode a wave of discontent to an upset Massachusetts US Senate victory in 2010 but was swept out of office in 2012, said Thursday he taking the plunge again, this time to the north.

Brown made official his bid to unseat New Hampshire US Senator Jeanne Shaheen and unleashed a fusillade of attacks on her record Thursday night. He knocked her vote in favor of the Democratic health care overhaul, said she had supported economic policies that hurt workaday people, and was a “rubberstamp” for President Obama.

“She’s a very nice person, but she’s wrong on the issues facing the people of New Hampshire,” Brown, 54, told a crowd of about 200 people in a Portsmouth hotel ballroom.

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“Is New Hampshire being well served by this out-of-step, out-of-touch Obama-Shaheen agenda?” Brown asked his supporters. “No!” they replied.

The tone of his speech, at once aggressive and warmly introductory, laid out what appeared to be two of the main thrusts of his campaign: tell voters why they should vote out Shaheen while explaining who he is to a state where he moved his primary residence last year.

Brown, who represented Massachusetts in the US Capitol as recently as January of 2013, played up his ties to Granite State, where he spent the earliest part of his life.

Traveling through the Portsmouth area, he said he passed by a lot of familiar spots.

“That includes, obviously, the river and the harbor, where my grandparents used to bring me when I was a boy,” he said, adding he had taken his daughters—who joined him on the stage—there as well.

Shaheen’s campaign manager, Mike Vlacich, released a statement in response to Brown’s announcement.

“If Scott Brown gets through the Republican primary, this election will be a choice between someone who cares only about himself and the big corporate interests that fund his campaign and someone who works every day to make a difference for New Hampshire families,” he said. “New Hampshire voters know Jeanne Shaheen shares their values.”

Democrats in New Hampshire say they see Shaheen, a former governor who won her first term in the US Senate in 2008, as well-positioned for victory.

State Democratic Party Chairman Ray Buckley, who was camped out near hotel where Brown gave his speech, said voters know Shaheen and vice versa. “She knows the state of New Hampshire. She’s been here. She knows the community,” he said.

While Brown faces a primary contest, state Republican operatives across New Hampshire said they believe, with a solid effort, Brown would emerge from the Sept. 9 election as the party’s nominee.

Dave Carney, a longtime GOP strategist, said Brown would have to work hard to get the nomination. But, “unless he screws up, I think he will,” he said.

Even at his kickoff, Brown appeared to have the imprimatur of support from GOP establishment: After one of his daughters, Ayla, sang the national anthem, he was introduced by former Governor John H. Sununu.

Sununu said Brown “will vote the way New Hampshire wants him to vote.”

“We’re here because we can count to 51,” he said, referring to the number of Senators needed for Republicans to take control of the legislative body.

Other Republican contenders in New Hampshire include former US senator Bob Smith, former state senator Jim Rubens, and conservative activist Karen Testerman. They have worked to run to the right of Brown, who, in 2012, framed himself as a common-sense moderate, who put Massachusetts interests over party orthodoxy.

On Thursday, he telegraphed that he understood the zeitgeist of his new home state, where an independent electorate is filled with voters who put an outsize emphasis on face-to-face contact with candidates.

Brown said he loved hearing from people across the state, even when they disagreed.

Carney, the strategist, said embracing retail politics would be essential for Brown.

“It’s very simple in New Hampshire. It’s not a lot of brain surgery,” Carney said. “People want to look you in eye, ask you questions, judge your character by your answers and move on from there.”

Brown upset Attorney General Martha Coakley in the 2010 Massachusetts special election race to succeed Edward M. Kennedy. In 2012, Democrat Elizabeth Warren unseated Brown, besting him by more than 7 percentage points.

The former Wrentham resident moved his primary residence to his summer home in Rye, N.H. last year and registered as a voter there in December. He announced he was exploring the US Senate race last month and has spent much of time on the campaign trail going after Shaheen. For her part, she has knocked him for refusing to sign a pact to limit outside spending in the race and said he represents oil interests and Wall Street.

Politicos expect an expensive campaign with negative attacks from both sides.

“That’ll be a doozy, that’s for sure. She’s a tough customer, I make no bones about it,” Republican state representative Gene Chandler, a former speaker of the House, said of Shaheen.

“It’ll be all-out war,” he said. “Ready for it or not, it’s coming.”