US president-elect Donald Trump has endorsed the niece of former foe Mitt Romney to be the next chair of the Republican National Committee.

Michigan Republican Party chair Ronna Romney McDaniel was named as the RNC's deputy chair, replacing Reince Priebus, who will become Mr Trump’s chief of staff.

Mr Trump said he looked forward to Ms McDaniel taking over the party leadership.

"I'm excited to have a highly effective leader in Ronna McDaniel as RNC deputy chair and I look forward to her serving as the party's chairman in 2017," Mr Trump said in a statement.

"Ronna has been extremely loyal to our movement and her efforts were critical to our tremendous victory in Michigan, and I know she will bring the same passion to the Republican National Committee," he added.

Her appointment has to be approved by the committee’s 168 members when they meet in January.

Mr Trump’s endorsement has likely boosted her chances of victory.

Ms McDaniel caught Mr Trump’s attention when she helped him to win the state of Michigan, the first time it voted Republican since 1988.

Donald Trump's controversial cabinet

Mr Priebus called her "an outstanding fundraiser" while Stephen Bannon, the founder of white supremacist website Breitbart and Mr Trump’s chief adviser, said she was "completely committed" to his boss and to ensuring a Republican "victory at all levels".

Two days prior to her appointment, Mr Trump was accused of "toying" her uncle Mr Romney for secretary of state.

His longtime adviser Roger Stone told Infowars that Mr Trump never had any intention of appointing Mr Romney, who called him a "fraud" and a "conman" a few months before.

Mr Trump instead appointed Exxon Mobil Corp CEO Rex Tillerson.