Andrea Leadsom has backed Boris Johnson to be the next Conservative Party leader.
Ms Leadsom, who was knocked out of the race in the first round of voting, said the frontrunner is "a proven election winner".
She told talkRADIO's Julia Hartley-Brewer: "I think he is most closely aligned to my own view on the importance of getting out of the EU at the end of October.
"I think he is a proven election winner and it is key for the country to keep Corbyn out and I think Boris will be able to do that and reunite the country.
"He can take the country forward in a positive way."
She added: "I am giving him my wholehearted and very loyal support."
Ms Leadsom suggested that the "uncertainty" surrounding Brexit was damaging the UK's economy.
"The point about this is that we need to move on," she said. "People and businesses need certainty."
The six remaining leadership hopefuls are set to face a second round of voting on Tuesday.
Candidates need to gain at least 33 votes from MPs to remain in the race to reach the final run-off, which will see some 160,000 Tory members select the next Prime Minister.
If all candidates pass the 33-vote threshold, the one with the lowest total will be eliminated.
Mr Johnson, who topped the initial poll with 114 votes, refused to take part in hustings with journalists on Monday, but is set to join rivals for a candidates' debate on the BBC on Tuesday evening.
The other contenders are; Rory Stewart, Sajid Javid, Jeremy Hunt, Michael Gove and Dominic Raab.