WAKEFIELD — Republican Richard R. Tisei, a former state senator who narrowly lost a bid to unseat US Representative John F. Tierney in 2012, said he will officially kick off his second campaign for Congress here on Thursday with a hometown rally and a Web video.

His announcement will mark the start of what is likely to be Massachusetts’ most competitive congressional race in 2014. The North Shore-anchored district, which stretches from Bedford to Rockport to Salisbury, is the state’s least Democratic.

Tisei, 51, occupies a unique place in the GOP. Openly gay, he is a supporter of abortion rights and gay marriage, as well as smaller government and lower taxes. He emphasized his moderate brand in an interview earlier this week, saying would put what was best for his constituents before his party affiliation.

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“I’m not going to become a combatant down in the partisan war that’s taking place in Washington, I’m going to do what’s best for the state,” Tisei said.

Over the hum of patrons eating breakfast at a diner in Wakefield on Monday, Tisei said his bid would be focused on the Affordable Care Act.

“I intend to make Obamacare the central issue of my campaign because I believe that no other state in the country has suffered more under Obamacare than Massachusetts,” he said.

Tisei argued that the sweeping federal law has hurt this state and that Massachusetts — which already had a universal health care statute on the books — should be exempt from it.

Tisei, who was his party’s nominee for lieutenant governor in 2010, said he did not know if the Affordable Care Act would be repealed, but thought it would be best for Massachusetts if Congress passed a new law exempting states in which more than 95 percent or 98 percent of people have health insurance coverage.

The announcement from Tisei, who has long been expected to make a second attempt to represent the Sixth Congressional District, could set up a re-match with Tierney, who won re-election by only one percentage point in 2012. The Congressman faces two primary opponents: Seth Moulton, a former Marine, and Marisa DeFranco, an immigration lawyer.

The 2012 race drew national political and media attention and millions of dollars in spending from outside groups on both side of the aisle.

Tisei, a longtime legislator and his party’s 2010 nominee for lieutenant governor, was seen as a particularly strong GOP contender in a state that has not elected a Republican to the US House since 1994. And Tierney was widely viewed as politically vulnerable, burdened by his family’s legal woes related to an illegal gambling enterprise run by one of his wife’s brothers.

Tierney, who has not been charged with any crime and has maintained that he has done nothing wrong, ultimately won the race.

But he was battered, in particular, by questions about $223,000 that his wife, Patrice, paid to herself in over a number of years while managing a joint bank account for one of her brothers, federal fugitive Robert Eremian, who was running an offshore illegal gambling enterprise.

At issue was whether the congressman should have reported that money as taxable income on his federal financial disclosure forms and tax returns. He and his wife insisted the payments were gifts and thus did not need to be reported

Tisei said his campaign would focus on Tierney’s record in Congress rather than on his family’s legal troubles.

Tierney, for his part, is seen by Democratic operatives as being in a stronger position than he was in 2012.

And he’s garnered visible support from key Democratic leaders. Tierney and US House Democratic leader Nancy Pelosi appeared together at a forum in Beverly in August and the congressman attended a high-dollar Democratic fund-raiser with President Obama in October, after flying into Boston with him on Air Force One.

Still, a Tierney aide said the campaign team was confident but expected a real general election fight.

Since his loss, Tisei said he had been focused on the real estate business he owns. He said he did not plan to be a different person for this election.

“I’m not going to reinvent myself. You know, I am who I am,” he said.

But there was one visible difference between Tisei of 2014 and Tisei of 2012: he was sporting a wedding band. Tisei married Bernard F. Starr, his longtime life partner, in July 2013.

The primary election is set for Sept. 9 with the general election on Nov. 4.