"As you know, after careful consideration and long discussion with my wife, Julie, we agree the time has come for us to move on from this part of our life," Chaffetz wrote in a letter posted on his social media. "This week I sent a letter to Governor (Gary) Herbert indicating my intention to resign from Congress effective June 30, 2017."
Chaffetz said last month he was not running for reelection, and then later said he might not finish out his term. He's reportedly eying a position at Fox News after leaving the House.
Chaffetz is head of a committee that is the House's investigatory arm into the Executive Branch. He has started digging into President Donald Trump's firing of FBI Director James Comey and the former director's memo saying Trump asked him to drop the investigation into former national security adviser Michael Flynn.
This week, Chaffetz sent a letter from FBI Director Andrew McCabe seeking all FBI notes and information on Comey's communications with Trump, and he announced a hearing next week where he's invited Comey to testify.
There's no indication yet, however, that the former FBI director plans to attend -- and Chaffetz had trouble reaching Comey.
Rep. Elijah Cummings, the top Democrat on the panel, has repeatedly clashed with Chaffetz during several investigations, but told CNN that he was "going to miss him" and that he brought a "breath of fresh air" to the committee after it went through some tumultuous times under prior Republican leadership.
Cummings said despite their differences they did work in a bipartisan way to address issues within the US Secret Service, postal reform, and the TSA.
Chaffetz' departure is likely to spark a battle over who replaces him as the head of the oversight committee that will once again pit the House Freedom Caucus against the establishment.
Rep. Jim Jordan of Ohio, a Freedom Caucus founder, said he's interested and expects he would have support of the committee members -- but he noted that the steering committee heavily controlled by Republican leadership will pick who gets the gavel.
"Let's be honest, you know the process for determining chairman is not a vote of the members on the committee, it's the steering committee," Jordan told reporters. "And that process is not always the one that's most favorable to guys like me who don't always go along with the establishment."
House Freedom Caucus Chairman Mark Meadows, who sits on the oversight committee, said he had not spoken to Chaffetz directly, but was aware of his discussions with others about plans to step down from Congress.
He backed Jordan to get the gavel, noting he's a longtime leader on the panel. When pressed if his role in the Freedom Caucus, which has clashed with the leadership could pose a strike against him in a contest for the post, Meadows admitted "of course it is."
Rep. Trey Gowdy of South Carolina, who led the House's Benghazi select committee, is considered the favorite to become the next oversight chairman.
Gowdy did not respond to questions about his interest in the gavel on Thursday as he entered the House floor for votes.