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Scott Brown, the former senator from Massachusetts, made it official this evening jumping into the U.S. Senate race against Sen. Jeanne Shaheen. Brown is attempting to get back to Washington, but this time from neighboring New Hampshire.

In his announcement speech, he noted the Granite State's "independent streak" and touted his own "independent spirit in action," making a "promise" to voters "I'm nobody's yes man."

"I will answer only to you, the people of New Hampshire," Brown said Thursday evening kicking off his official campaign in in Portsmouth. "Every day that I serve, I will give the job all that is in me."

Brown has a GOP primary in September, but is heavily favored to go on to battle Shaheen, a Democrat, in a fight that has quickly become one of the most widely watched since he began flirting with entering the race and one that is likely to become the most expensive in New Hampshire history.

In a campaign where he is already being called a "carpetbagger," Brown stressed his roots in New Hampshire-noting he was born in the state and his parents met there-as well as his time spent on the road the last few weeks since he announced his exploratory committee last month.

In his introduction, former Gov. John Sununu actually brought up the Bay State, calling Shaheen the "third Senator" from Massachusetts accusing her of a liberal voting record.

The announcement was highly anticipated. Brown moved into his Rye, N.H., vacation home full time last year, putting up his home in Wrentham, Mass., for sale in September. He surprised the country when he won in 2010 to fill Ted Kennedy's seat after his death, but two years later, he lost to Elizabeth Warren by almost 8 percentage points.

As he did in his 2010 race, Brown stressed his opposition to the Affordable Care Act and pinned it on his opponent saying, "whenever President Obama needs her, she's there, and apparently he needs her a lot."

Brown predicted the worst is yet to come and said to cheers from the crowd it forces people to "make a choice, live free or log on."

Despite his focus on Obamacare, he did not mention the news that broke just moments before he took the stage, that Health and Human Services Secretary Kathleen Sebelius would step down Friday.

From Obamacare to foreign policy, Brown previewed how nasty the battle is likely to get. Although he called his opponent "very nice," he repeatedly compared Shaheen to President Obama, accusing the senator and also former governor of New Hampshire of being a "rubber stamp" for the president.

"President Obama's weakness and indecision has emboldened our enemies and discouraged our allies," Brown said. "There is a sense we are losing influence and the ability to shape events…I want a strong America. I don't want one that leads from behind. I want one that is respected by friend and foe alike."

Longtime New Hampshire Republican strategist and treasurer for the New Hampshire GOP Jim Merrill said Brown's entry undoubtedly "changes the landscape for Democrats in 2014," mentioning the battle they have to hold on to the Senate, but also noted Brown has a primary first and his opponents will give Brown "a run for his money."

Merrill counseled Brown to "focus" on his primary and then he will be in a good position in the general election.

"Scott Brown is a familiar figure here in New Hampshire," Merrill said in an interview with ABC News, noting their shared media market. "There is an awful a lot of connections between New Hampshire and Massachusetts. Scott Brown can't take (the primary) for granted, but he certainly appears to want to work hard and earn the vote."

Shaheen campaign manager Mike Vlacich responded to Brown's announcement saying, "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."