Denver, Colorado - A US election denier whose case has been championed by Donald Trump was granted a commutation Friday that will see her released from state prison next month.

Tina Peters, a former official in Colorado's Mesa County, was sentenced to nine years for allowing an unauthorized Trump supporter to access confidential voting information several months after Joe Biden won the 2020 election.

The man was seeking to prove election fraud as part of a conspiracy theory touted by Trump that the vote was rigged.

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Colorado Governor Jared Polis, a Democrat, on Friday told Peters he was cutting her sentence by more than half.

"The crimes you were convicted of are very serious, and you deserve to spend time in prison for these offenses," he wrote to her.

"However, this is an extremely unusual and lengthy sentence for a first-time offender who committed nonviolent crimes."

The commutation to four years and 4.5 months means Peters will be released on parole on June 1.

Trump – who still refuses to accept that he lost the 2020 vote – has advocated for Peters, whom he calls "a patriot," to be released.

Last year, he granted her a symbolic pardon, as the US president has no power to forgive crimes that were prosecuted in state courts.

"Democrats have been relentless in their targeting of TINA PETERS, a Patriot who simply wanted to make sure that our Elections were Fair and Honest," Trump wrote at the time.

On Friday, shortly after news of her commutation emerged, he posted: "FREE TINA!"

Since taking back the White House in January last year, Trump has moved to expunge stains around his election denialism and the people who supported it.

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Most significantly, he granted clemency to nearly all of the 1,600 people convicted in connection with the January 6 assault on Congress by supporters seeking to block Biden's confirmation as the 2020 election winner.

Polis' move, which occurred amid a raft of other clemency issues, comes as Democratic Colorado continues to be in Trump's crosshairs.

The president has cut hundreds of millions of dollars in federal funding for the state, as well as begun dismantling a climate research center there.