Trade minister Sir James Duddridge said the man who stood down six weeks ago after being ousted by his own cabinet following a series of scandals has told him “we are going to do this”.
The Tory MP said Mr Johnson will land back in Britain on Saturday and will challenge to replace Liz Truss as Conservative leader.
But the development will not be welcomed by all Tories, with former leader Lord William Hague warning Mr Johnson’s resurrection would lead to a “death spiral” for the party.
Sir James, who served as one of Mr Johnson’s parliamentary private secretaries at No 10, told the PA news agency: “I’ve been in contact with the boss via WhatsApp.
“He’s going to fly back. He said, ‘I’m flying back, Dudders. We are going to do this. I’m up for it’.”
The MP for Rochford and Southend East was confident that Mr Johnson will get the 100 nominations from Tory colleagues to make it to the next stage of the contest “quite quickly”.
Commons Leader Penny Mordaunt is the only candidate who has officially declared she is running, but former chancellor Rishi Sunak is also expected to launch a challenge.
Sir James said Mr Johnson will argue he is “the only person that’s got a mandate” from the 2019 general election and that he can “bring the party together”.
Mr Johnson has “learned and reflected” during less than two months out of office, and knows he needs a No 10 operation that is “slicker” and has “command of the details”, according to the ally.
Sir James said Mr Johnson knows he needs a “government of all talents” and would “welcome back with open arms” even those who “said despicable things about him”.
Mr Johnson was picking up support from Cabinet ministers, including Jacob Rees-Mogg, Anne-Marie Trevelyan and Simon Clarke.
But Lord Hague, a Tory peer, said Mr Johnson returning is “possibly the worst idea I’ve heard of” during his 46-year party membership.
I think it's possibly the worst idea I've heard of in the 46 years I've been a member of the Conservative Party— Lord Hague
“I think it’d be a very, very bad idea to bring Boris Johnson back,” he told Times Radio.
“This all started, this unravelling, because Boris Johnson was unable to run the government in the right way, to keep it together in the right way, to uphold the high standards of conduct that are necessary in the highest offices in the land.
“Him returning is the solution? That would be going round in circles and that could become a death spiral of the Conservative Party.
“And I think it’s possibly the worst idea I’ve heard of in the 46 years I’ve been a member of the Conservative Party.”
Former minister Johnny Mercer said he could not put himself or his constituents through another Johnson administration after the “terrible” lows of the last time, as he backed Mr Sunak.
“Boris is a friend of mine, I love him to bits, he’s a great guy, but I just don’t think I can put myself through that again. I don’t think I can ask my constituents to, I don’t think I can ask my staff,” Mr Mercer told BBC Radio 4’s PM programme.
“I love Boris to bits and he’s got amazing qualities for this country, but it is now time for serious, competent, straightforward and values-based governance.”
A return for Mr Johnson would be beset with challenges, not least the inquiry into whether he lied to the Commons over the partygate scandal, for which he was fined by police.
If found guilty by the Commons Privileges Committee, he could face recall proceedings that would leave him battling for his seat in the Commons if he receives a suspension of 10 days or more.
His popularity with the public has crashed, even if he still rides high with the Tory membership.
Some MPs have even suggested they could resign the party whip if he wins.