After his endorsement, Baker will campaign with Christie in New Hampshire over the weekend, the people said. In Baker, Christie gains the support of a popular northeastern Republican governor the campaign hopes will punch momentum into a contest that he has referred to as the "last stand" of his presidential campaign.
Baker joins Maine Gov. Paul LePage as statewide office holders who have gotten behind Christie's bid.
Sam Smith, a Christie spokeswoman, declined to comment on the endorsement. Tim Buckley, a Baker spokesman, didn't respond to repeated calls requesting comment.
Christie has tried to lock down Baker's for months, according to people familiar with the matter. The two became close during Baker's 2014 run for the governor's office, when he flipped the state back into the Republican column with the help of $11.4 million from the Christie-run Republican Governor's Association
Christie attended Baker's inauguration and aides say the two, as Republican governors in traditionally Democratic states, have remained closely aligned over the last year. They were at a Bruce Springsteen concert together in Boston on Thursday night.
Baker provides a window into what Christie is counting on if he can achieve a strong showing in New Hampshire: the support -- and access to -- the finance networks of the governors he helped win election or re-election during his time atop the RGA.
Baker has his own robust finance operation, raising $2.4 million in his first year in office
, according to the Massachusetts Office of Campaign and Political Finance.
He is expected now to try and help steer those donors toward Christie.
"We have the organization of governors across this country," Christie told reporters Wednesday. "I believe that when I emerge as the top governor from New Hampshire, that those governors will come in line and begin to support the idea of having a governor" as GOP candidate.
For Christie, who has staked his campaign on his New Hampshire performance, Baker's endorsement adds a boost to an operation that is relying on a top tier performance in the state to vault Christie into the top tier of GOP candidates coming going into the South Carolina primary.
Christie sank to 4% in the latest CNN/WMUR New Hampshire tracking poll, falling behind Donald Trump, surging Florida Sen. Marco Rubio, Ohio Gov. John Kasich and former Florida Gov. Jeb Bush.
Christie himself has spent more than 70 days in New Hampshire this election cycle and has held more than 150 events.
Polls showed that work paid was paying off earlier this year, as Christie began a steady climb into the top tier of candidates not named Trump.
But that rise also drew the attention of his competitors and three weeks and million of dollars in attack ads later, Christie has seen his unfavorability ratings rise in the state and his poll numbers settle into the mid-single digits.
Christie has spent the last few weeks pointing out that the numbers have been fluid throughout the state -- on any given day, any of the so-called "establishment" candidates in the race are up or down -- and that the polls are unreliable. Nearly 60 percent of likely Republican voters hadn't firmly decided on a candidate in the CNN/WMUR poll
An open primary adds another potential surprise element into the mix.
Yet Christie has faced a new challenge in the final days before New Hampshire in the rise of Florida Sen. Marco Rubio, who has used a stronger-than-expected showing Iowa to bolster his own chances in the state.
Christie has spent much of this week attacking Rubio, calling him inexperienced and seeking to peg him as too conservative on abortion for the New Hampshire electorate. Still, even with the steady barrage of Rubio attacks, Christie and his team are sticking to the metric of success as finishing first among the governors -- Christie, Bush and Kasich.