"I have long advocated public service should be for a limited time and not a lifetime or full career", he wrote.
While Chaffetz left unclear what his future in public life might be, he could run for governor of Utah in 2020.
"For those that would speculate otherwise, let me be clear that I have no ulterior motives", Chaffetz added.
"I am healthy. I am confident I would continue to be reelected by large margins".
"Serving is an honor and a privilege that I have never taken for granted", Chaffetz said in a Facebook post.
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He reaffirmed US support for the freedom of navigation and trade though the South China Sea. Mr Trump has said the trade abuse probe will crack down on "foreign importers that cheat".
Representative Chaffetz said he chose to announce his intention not to run for re-election now to allow fellow Republicans the time necessary to develop the essential groundwork and campaign apparatus necessary to win the race. The longer you spend in Washington, the worse off you are; for every year there, it becomes that much tougher to get away from the DC stench in the minds (and noses) of Republican voters. He did not mention those possibilities in announcing his decision to leave the political arena, just five months after his re-election to Congress for a fourth term.
While Chaffetz's decision removes a high-profile foe of House Democrats, the seat he will vacate does not appear ripe for pickup. But Chaffetz could also be taking a hiatus from the political scene before a gubernatorial run in 2020, something he reportedly expressed interest in a year ago.
During his chairmanship, Chaffetz investigated former Secretary of State Hillary Clinton for her use of a private email account and server while conducting State Department business. At a town hall in February, Chaffetz was essentially booed for an hour straight, and a new billboard in his hometown of Provo questions the congressman's reluctance to investigate Russia's meddling in USA elections. "He's very rich. I don't think that he ran for this office to line his pockets even more".
Utah's 3rd District has always been reliable for Republicans: Chaffetz was elected with 66 percent of the vote in 2008; in his subsequent re-elections, he has easily garnered over 70 percent.
Chaffetz, 50, was elected to the House in 2008.