Mel Stride will announce his candidacy in the Conservative leadership race to replace Rishi Sunak on Friday.
The former work and pensions secretary says he has the backing of the 10 MPs needed to progress to the next stage of the contest.
Earlier this week, the central Devon MP said he was considering standing after “a number of colleagues” suggested he should.
He becomes the fourth person to throw their hat in the ring after former Home Secretary James Cleverly and former Home Office ministers Tom Tugendhat and Robert Jenrick.
Mr Stride was a close ally of Mr Sunak during the last government and was frequently trusted to do media interviews during the election campaign.
In the election on 4 July, he held on to his Devon constituency, an area he has represented since 2010, by just 61 votes, narrowly avoiding a defeat to Labour.
Speaking on election night, Mr Stride said the party needed to “think long and deeply about what has happened over the last 24 hours and get ourselves back in a position where we are the natural party of government”.
“But that is going to take time.”
Leadership hopefuls have until Monday to collect 10 nominations from their fellow MPs.
Those that clear that bar will then have the summer to make their pitches, before MPs vote to narrow down the candidate list to four, and then two.
Party members will then get to vote on the final two, with the results expected on 2 November.
Mr Sunak will stay on as leader until his successor is chosen.
