The former London mayor –who led the campaign for Britain to leave the EU only to see his own hopes of the leadership dashed following a devastating attack by Michael Gove – praised the Energy Minister as “level-headed, kind and trustworthy”.
“Andrea Leadsom offers the zap, the drive, and the determination essential for the next leader of this country,” he said in a statement.
The news came last night hours before today’s vote as contenders frantically try to amass enough backing from MPs to challenge Theresa May.
The Home Secretary is the favourite candidate among members so far, with 97 MPs publicly backing her.
Mr Gove was overtaken by Mrs Leadsom as the second most popular candidate but the Justice Secretary remains intent on making the final two on the ballot paper that eventually goes out to party members.
Meanwhile, Nigel Farage has stepped down as Ukip leader with Yorkshire Ukip MEPs calling for “official recognition” for him.
Jane Collins and Mike Hookem claimed Mr Farage’s long campaign for a departure from the European Union had given the British people their voice back.
Some Ukip supporters have suggested Mr Farage should be given a peerage in the aftermath of last month’s referendum decision to leave the EU.
Voting underway: Page 4.