"But every good fighter knows when to hang up the gloves, and for me, that time is soon approaching".
Romney, the former MA governor who now lives in Utah, has been eyeing a Senate run, but President Donald Trump had encouraged Hatch to seek re-election.
Mr. Hatch's decision clears the way for the political resurrection of Mr. Romney, the former MA governor and 2012 Republican presidential nominee who is now a Utah resident and is popular in the Mormon-heavy state.
Hatch is the second-longest serving current US senator, serving for more than 40 years.
Romney did not have an immediate public reaction to Hatch's announcement.
Hatchs decision comes just weeks after Trump signed a sweeping tax overhaul into law, a measure that the senator helped write as chairman of the Finance Committee. In a very statesman-like way, Romney said Hatch "represented the interests of Utah" with honor and distinction.
Romney, who sought the GOP nomination in 2008 and got it in 2012, also laid into Trump during that speech for "the bullying, the greed, the showing off, the misogyny, the absurd third-grade theatrics".
New Orleans Saints 14, Tampa Bay Buccaneers 13
Saints defensive end Cameron Jordan picked up his 13th sack of the season, on a play that ended the first half. The Bucs went 95 yards from their own 5-yard line without a timeout in less than two minutes.
Mr Romney has been quiet about his plans and views of late.
Late past year, Hatch also found himself in a heated debate with Democratic Sen.
Hatch, 83, was first elected in 1976 and had spent months publicly deliberating about whether to stand again for reelection in November. Last month, Trump flew with Hatch on Air Force One to Utah for a day of events that was aimed entirely at lobbying the senator to run again.
Utah is a great state for Romney and a bad one for Bannon, which means that the former White House chief strategist would be under little pressure.
Other conservatives in the state have been trying to recruit another conservative challenger to contest Romney from the right, but no candidates have yet come forward. Sherrod Brown of OH after Brown said Republican tax cuts were aimed at helping the rich.
If Hatch had opted to stay in the Senate, he could have faced a formidable challenge from a crop of ambitious Utah Republicans.
In the statement announcing his decision to retire, Hatch cited work helping create the Americans with Disabilities Act, expanding children's health insurance and expanding use of generic drugs. Hatch earned about $39,000 in royalties from his songs in 2005.