While she is the first serving minister to endorse her former boss’ chief rival in the contest, Ms Badenoch is one of several former Johnson allies to switch camps.
Other senior figures to the party’s right have given him a firm lead in the competition, although he is yet to formally declare his candidacy.
Lord David Frost, the former Brexit secretary, backed the ex-Chancellor this afternoon.
Lord Frost heaped praise on the former Prime Minister, but warned it was time for the Conservatives to change path.