Mr Ellwood had lost the party whip after he failed to support the Government in the confidence vote on Monday.
But today he wrote on Twitter: "Delighted to report my request for a momentary return of the whip has been granted – just long enough for my proxy vote to be cast!"
His return could have significant ramifications for the shape of the Tory leadership race, given his support for Ms Mordaunt.
With Rishi Sunak practically guaranteed a place in the run-off vote of Tory party members, who choose between the final two candidates, it is only Ms Mordaunt standing between Liz Truss and her place in the next decisive stage of the contest.
Tobias Ellwood House of Commons
Conservative Party leadership contender Penny Mordaunt Victoria Jones
The former minister and chairman of the Commons Defence Committee had argued he was unable to travel back from a meeting with the president of Moldova.
He said today that recent weeks have been a “sad chapter” in the history of the Conservative Party, warning that they have "lost" their "way".
The restoration was to ensure the neutrality of the Whips Office “can not be questioned”, a spokesperson said.
A Whips Office spokesperson said: “From the start of the leadership contest the Whips Office took a neutral position.
“After Tobias Ellwood MP failed to attend an important vote he had the Conservative Party whip suspended.
“To ensure that the Whips Office neutrality in the leadership contest can not be questioned, the Whip has been temporarily unsuspended from Tobias Ellwood MP.
“Upon the conclusion of today’s leadership contest, Tobias Ellwood MP will have the whip suspended.”
Government minister Simon Clarke had previously defended the decision to strip the whip from Mr Ellwood.
Mr Clarke said Mr Ellwood has made a “very serious mistake”, adding: “He was in Moldova, rather than Ukraine.
"He was not on Government work, he is a backbench MP.”