An election-denying former mixed martial arts fighter who was widely criticised for an attempted freelance mission last year to rescue Americans trapped in Afghanistan has won a shot at a US Senate seat from Oklahoma.

Markwayne Mullin, a sitting congressman, beat another Donald Trump loyalist and election denier for their party’s nomination in a special election on Tuesday and will seek to replace the long-serving senator Jim Inhofe in November.

Mullin, a plumbing company owner from Westville, and TW Shannon, a former speaker of the Oklahoma House and a bank executive from Oklahoma City, both embraced Trump’s lie that the 2020 presidential election was subject to widespread fraud.

The two were the top finishers in a 13-candidate Republican primary in June, but neither topped the 50% threshold needed to win the nomination outright.

Mullin, who topped that field with nearly 44% of the vote, earned Trump’s endorsement shortly after the primary. He has something else in common with the former president: an exaggeration of his own sporting prowess.

The politician who declared “I’m not Rambo” after his much-ridiculed attempt to enter Afghanistan in the company of a private US security team, boasts on his website a 5-0 record as a professional mixed martial arts fighter.

The official record of his short-lived career suggests a different story: a total of three wins, two against the same opponent, and cumulative fight time of less than 10 minutes in under three rounds.

In the political ring, Mullin will now seek to replace the retiring 87-year-old Inhofe, a fixture in Republican politics in Oklahoma since the 1960s who has held his Senate seat since 1994. Inhofe is leaving before his six-year term is finished, so his replacement will serve four years.

In November, Mullin will be heavily favored to beat the former Democratic congresswoman Kendra Horn, along with an independent candidate and a Libertarian. Oklahoma has not elected a Democrat to the US Senate in more than 30 years.

In a state where nearly 10% of the population identifies as American Indian, both Mullin and Shannon are members of Native American tribes. Mullin is a Cherokee citizen and Shannon, who is also African American, is a citizen of the Chickasaw Nation.

Campaign finance reports showed Mullin raised about $3.6m, nearly three times the $1.3m Shannon reported.

In campaign ads and on the stump, both touted their positions on hot-button issues and vowed to fight Joe Biden’s agenda.

Shannon launched an anti-abortion ad in which he labeled Planned Parenthood the “true face of white supremacy”. Mullin, in an ad featuring two of his own children and a montage of the transgender collegiate swimmer Lia Thomas, said: “Democrats can’t even tell us what a woman is.”

Also on Tuesday, in the Democratic primary runoff for Oklahoma’s other US Senate seat, the cybersecurity expert Madison Horn defeated Jason Bollinger, an Oklahoma City attorney.

Horn, who is not related to Kendra Horn, will face the incumbent Republican senator, James Lankford, who will be the heavy favorite in November, along with a Republican and an independent.