Mr. Kelly, who is facing a tough reelection campaign this year, said the decision stemmed from his belief that the 60-vote threshold should not stand in the way of President Biden’s rewrite of the nation’s election laws.
The announcement comes as Senate Majority Leader Charles E. Schumer has pledged to bring a vote on changing the filibuster after Mr. Biden’s partisan voting measures are defeated by Republicans this week.
Mr. Schumer, New York Democrat, is proposing a requirement that lawmakers mount an old-fashioned “talking filibuster” to hold up the legislative process.
Under the proposal, senators would need to speak continuously in objection to a bill. Once the speechmaking is exhausted, the legislation could pass with a simple majority vote.
Currently, lawmakers are allowed to merely object to ending debate, forcing leaders to round up the 60 votes to keep the legislation alive.
“Win, lose or draw, members of this chamber were elected to debate and to vote, especially on an issue as vital to the beating heart of our democracy as voting rights,” Mr. Schumer said.
For any rules change to succeed, the unanimous support of all 50 Senate Democrats is needed in the evenly split chamber.
The push is all but doomed to fail after a key swing vote, Sen. Joe Manchin III, came out in opposition. Mr. Manchin, West Virginia Democrat, argued that the talking filibuster would be useless without the 60-vote threshold required to end debate.
“I love the talking filibuster, I think we should be transparent about how we do business here or the lack of doing business,” he said. “In the history of our country, there has never been a simple majority vote to [end] debate. … I don’t know how you break a rule to make a rule. We’ve never done this.”
Last week, Ms. Sinema pledged to oppose any weakening of the filibuster, claiming it would only further the “diseases of division.”
“Eliminating the 60-vote threshold on a party-line [vote], with the thinnest possible majorities, to pass these bills that I support will not guarantee that we prevent demagogues from winning office,” Ms. Sinema said.
Mr. Kelly’s announcement ends weeks of speculation about his stance on the filibuster. He initially campaigned as a moderate in a 2020 special election to fill the seat vacated by the death of Republican John McCain. Throughout the race, Mr. Kelly refused to take a position on the filibuster.
“I’ve considered what rules changes would mean not just today, but years down the road, for both parties and all Arizonans,” he said. “If campaign finance and voting rights reforms are blocked again this week, I will support the proposed changes to pass them with a majority vote.”