Retiring Sen. Olympia Snowe (R-Maine) will back fellow centrist Sen. Scott Brown (R-Mass.) in his reelection bid.
"In an institution characterized by gridlock and partisanship, Scott Brown is a much-needed breath of fresh air," Snowe will say in a statement later on Thursday.
A centrist Republican senator poised to easily win reelection in November, Snowe shocked her colleagues in February by announcing she would retire at the end of her term. She cited the partisanship and gridlock that has altered the nature of the Senate, and sought to portray Brown as a Republican willing to work across the aisle.
"As I leave the Senate, it is my deep hope that this institution and America will continue to benefit from the thoughtful leadership of Scott Brown and others who favor progress over partisanship," Snowe said in endorsing Brown.
Brown said he was committed to looking past party to address the nation's challenges.
"She has served as an example to those of us who prefer bridge-building over rock-throwing," Brown said of Snowe.
Elected in a 2010 special election to replace the late Sen. Edward Kennedy (D-Mass.), Brown has maintained strong popularity in Massachusetts despite being the only Republican in the state's congressional delegation.
Part of that popularity has stemmed from his reputation as an independent figure who has parted with his party on major issues. Those credentials have been key to the success of other Republican senators serving in Democratic-leaning states, such as Snowe and Maine's other senator, Republican Susan Collins.
But Brown faces a vigorous and deep-pocketed challenge in his bid for a full term from Democrat Elizabeth Warren, whose campaign has captured the attention of Democrats across the country. Recent polls show Brown with a single-digit lead over Warren.
Snowe and Brown both serve on the Senate Committee on Small Business and Entrepreneurship.