But during exchanges in the Commons yesterday he congratulated Mrs May and backed her premiership.
He said: “May I congratulate the Prime Minister on winning the confidence of the Conservatives in this House last week and assure her that she therefore commands my confidence too.”
Mr Rees-Mogg, the chairman of the European Research Group, hinted last month he would submit a letter of no confidence in the premier during exchanges at Prime Minister’s Questions.
In a letter, he accused Mrs May of failing to stick to her pledges over Brexit.
After Mrs May won the confidence vote last week, Mr Rees-Mogg described the result as “terrible”.
He claimed the PM had “clearly lost the support of the back benches of the Conservative Party” and “that was not a good position for her to be in”.
“She ought to go and see the Queen urgently and resign,” he said.
Mr Rees-Mogg explained his surprise change in tack by putting his comments down to festive cheer.
“At Christmas it is wrong to be a dog in the manger, that is where a baby belongs,” he said.
A stony-faced Mrs May thanked him for his support as she updated MPs on Brexit.
May leadership challenge ‘happened twice’
Tory MPs pulled the trigger on a leadership challenge against Theresa May twice in one day, the MP in charge of the contest has revealed.
Sir Graham Brady said the number of letters needed to launch a confidence vote in the Prime Minister was first reached last Tuesday morning – only for one Tory to have a change of mind.
The tally then reached the crucial 48 figure again later that afternoon and Sir Graham, the chairman of the 1922 Committee of backbench Tory MPs, asked for a meeting with Mrs May to tell her of the challenge.
But the development was leaked and Sir Graham suggested senior figures in the government responsible did not have the PM’s “best interests at heart”.
Sir Graham had kept the number of Conservatives who had registered that they wanted a challenge against Mrs May a closely guarded secret.
The critical threshold was reached last week after Mrs May decided to pull a crucial parliamentary vote on her Brexit deal.
Sir Graham told how one MP approached him saying he did not want to hand over a letter but just could not “leave it any longer”.
Writing in The House magazine, he added: “A House of Commons envelope travelled from his inside jacket pocket to mine in a matter of seconds. Unseen, the trigger had been pulled. Lots of people have congratulated me on my poker face recently but never had it been more important that I remain impassive: any sign that this was a critical moment would have changed the whole dynamic of the process, so I bade the colleague farewell and walked quickly back to my office.
“Time for a final count and to plan the next steps. The door had barely closed when there was a knock on it… standing there was a Conservative MP who had submitted a letter to me a couple of weeks before. ‘The timing is just bloody awful, I’d like to withdraw my letter,’ they said. Back to 47.”
But he went to see Mrs May later that day when the threshold was crossed, saying she was “keen to get on with it and clear the air”.
Westminster was “buzzing” with the news before the call, but Sir Graham insisted he was “confident that my office doesn’t leak”.
“But someone did,” he said. “Could it have been someone within the government machine who didn’t have the Prime Minister’s best interests at heart?” He added: “It may be that the immediate cause was the decision to defer the vote on the EU Withdrawal Agreement, but I am sure that going ahead and losing the vote by a massive margin would have had exactly the same effect.”
Mrs May won the confidence vote 200 to 117 and cannot be challenged by her party now for another year.