U.S. Sen. Jim Inhofe, a Oklahoma Republican who has served in Congress since 1987, will not complete the remainder of his Senate term and will instead retire next January, two sources confirmed to Fox News. 

Inhofe, 87, privately announced the decision to his staff and elected officials Thursday. He was expected to make his retirement plans public as soon as Friday, the sources said.

Sen. Jim Inhofe

Sen. Jim Inhofe, R-Okla., in the Dirksen Senate Office Building in Washington, Sept. 28, 2021. (Getty Images)

The timing of Inhofe's announcement is related to a new Oklahoma state law that requires the state to hold a special election if a lawmaker announces a retirement before March 1. 

SEN. JAMES INHOFE: BIDEN'S CLIMATE FIATS AREN'T ABOUT CLIMATE—THEY'RE ABOUT CONTROL

The two sources told Fox News that Inhofe's chief of staff, Luke Holland, is expected to run for the seat with Inhofe's expected endorsement. 

Other potential candidates are GOP Reps. Markwayne Mullin and Kevin Hern; T.W. Shannon, the former speaker of the Oklahoma House of Representatives; and Gentner Drummond, who previously ran for attorney general, one source told Fox News. 

MCCONNELL, BRAUN CALL FOR INVESTIGATION INTO CHARITABLE BAIL ORGANIZATIONS RECEIVING TAXPAYER DOLLARS

The special election would be held this year with a primary on June 28, primary run-off on Aug. 23, and a general election on Nov. 8. The newly elected senator would take office just as Inhofe steps down so as not to leave a vacancy in the 50-50 split Senate, according to the sources familiar with Inhofe's plans.

Vice President Joe Biden greets Sen. James Inhofe and his wife Kay Inhofe after a Senate re-enactment swearing-in ceremony in Washington, Jan. 6, 2015. (Associated Press)

Vice President Joe Biden greets Sen. James Inhofe and his wife Kay Inhofe after a Senate re-enactment swearing-in ceremony in Washington, Jan. 6, 2015. (Associated Press)

Inhofe started serving Congress in Washington in 1987 in the House of Representatives and was elected to the Senate in 1994. He's the top Republican on the Senate Armed Services Committee. 

Inhofe was last elected in 2020 with 63% of the vote, and his term would have ended in January 2027.

CLICK HERE TO GET THE FOX NEWS APP

The Senate seat in conservative Oklahoma is expected to stay in GOP hands. 

Inhofe's early retirement news was first reported by The New York Times. 

His office did not respond to requests for comment.