Mel Stride will replace Andrea Leadsom, after she quit as Commons leader in a bid to topple Theresa May .
Ms Leadsom's resignation has sparked a mini-reshuffle - as Mrs May promoted a string of junior ministers to fill the role.
Mr Stride, a Remainer, will be promoted from his previous roles as Financial Secretary to the Treasury and Paymaster General.
He will be replaced by Jesse Norman, who moves from the Department of Transport, where he was a junior minister.
Mr Norman will be replaced by Michael Ellis who was previously Parliamentary Under Secretary of State at the Department of Digital, Culture, Media and Sport.
And Mr Ellis will be replaced by Taunton Deane MP Rebecca Pow.
Asked if it was time for Prime Minister Theresa May to resign, Andrea Leadsom told reporters: "Well, that's a matter for her.
"But, for me, I felt I couldn't in all conscience stand up and deliver the business statement today with the Withdrawal Agreement Bill in it that I couldn't support elements of.
"So, I have no doubts that I made the right decision and, of course, it's for the Prime Minister to decide what's right for her and for the country."
She declined to answer if she would run for the leadership.
