Nikki Haley is dropping out of the US presidential race, a source familiar with the matter told Reuters on Wednesday.
The decision will ensure that Donald Trump will win the Republican nomination and once again face Democratic President Joe Biden in November's election.
Haley, a former US Ambassador to the United Nations, is expected to make an appearance to deliver brief remarks in the Charleston area of South Carolina around 10 a.m. ET (1500 GMT).
She will not announce an endorsement on Wednesday, the Wall Street Journal said, but will encourage Trump to earn the support of Republican and independent voters who backed her.
Haley was Trump's final Republican opponent
Haley was Trump's last remaining rival for the Republican nomination.
On "Super Tuesday," Trump won the Republican votes in 14 of 15 states - including delegate-rich California and Texas - brushing aside Haley, whose only win of the night came in Vermont.
The Journal said that Haley was expected to emphasize that she will continue to advocate for the conservative domestic and foreign policies she supports and caution against some of the dangers, such as isolationism and a lack of fiscal discipline, that she sees coming from Washington.