Penny Mordaunt, the leader of the House of Commons, has become the first person to announce her candidacy for the Conservative party leadership – her second such attempt this year. Mordaunt, a former defence secretary, was ousted from the year’s first Tory leadership contest in the fifth round, losing out to Rishi Sunak and Liz Truss. Announcing her bid on Friday, Mordaunt tweeted: “I’ve been encouraged by support from colleagues who want a fresh start, a united party and leadership in the national interest. “I’m running to be the leader of the Conservative party and your prime minister – to unite our country, deliver our pledges and win the next GE [general election].” Mordaunt is not considered the frontrunner but has about 19 public endorsements. She is likely to hope that formally declaring her candidacy could trigger enough people to swing in behind her before the deadline to reach 100 Tory MP supporters by 2pm on Monday. The former chancellor Rishi Sunak and ex-prime minister Boris Johnson are considered the leading candidates. If Mordaunt trails behind them, she could become the kingmaker by giving her support to one of the others and taking many of her backers with her. She previously came third in the last leadership contest behind Truss and Sunak in second place. Her supporters include Maria Miller, a former culture secretary, and Andrea Leadsom, a former business secretary and ex-leadership candidate against Theresa May. Mordaunt is considered to be on the liberal wing of the Tory party but also supported Brexit.