Dame Priti Patel has said she can unite the Tories and turn them "back into a winning machine" as she launched her bid for the party's leadership.
The former home secretary said her political experience meant she would be able to "reinvigorate" the party following its recent election defeat.
“I have done this throughout my 30 plus years of service to our Party, in both government and opposition. I can get us match fit to win the next general election.”
Dame Priti is the first woman to throw her hat into the ring to replace Rishi Sunak, and joins James Cleverly, Robert Jenrick, Tom Tugendhat and Mel Stride.
The 52-year-old was widely expected to run for the leadership. Other people who are expected to join her but have not yet declared include the shadow communities secretary Kemi Badenoch and Suella Braverman, another former home secretary.
Dame Priti has been a backbench MP since stepping down as home secretary in 2022, following the resignation of her ally Boris Johnson.
She has been highly critical of the Conservative Party's leadership in recent years, blaming them for the Tories' slide from political favour that culminated in July's historic election defeat.
"It isn’t our heroic members who failed, but politicians’ distraction from public service," she said on Saturday.
“It is time to put unity before personal vendetta, country before party, and delivery before self-interest."
Dame Priti added that one point of difference between her and other leadership candidates was that she would reward members' dedication by giving them more of a voice in the party.
She also said that it would be through focussing on conservative policies on issues including law and order, immigration and healthcare that would reverse the party's fortunes.
“We must now turn our conservative values into strong policies to bring about positive change for people across our country."
Dame Priti, who retained her seat in the Essex constituency of Witham in the recent general election, is a Eurosceptic who was a leading figure in the Vote Leave campaign during the EU referendum.
She has previously taken a leading role in negotiations with France over immigration and played a key role in drawing up a new post-Brexit points-based system.
The MP has also faced allegations of bullying. In 2020, a Cabinet Office inquiry into her conduct found that Ms Patel had "unintentionally" breached the ministerial code in her behaviour towards civil servants.
Her "approach on occasions has amounted to behaviour that can be described as bullying," the government's independent advisor on standards said at the time.
Mr Johnson, who was then prime minister, decided Dame Priti had not broken the ministerial code and could remain in her post as home secretary.
He awarded her a damehood in his resignation honours last year.
Dame Priti also served in Theresa May's cabinet as secretary of state for international development and was Lord Hague's press secretary from 1997 to 2000 after he became the leader of the Conservatives.
Rishi Sunak will remain Conservative leader until his successor is announced.
The process to choose his replacement will see Tory MPs whittle down the field of candidates who secure enough backers to four by the time of the party's annual conference in Birmingham at the end of September.
In a series of further ballots, the MPs will then narrow the field to a final two contenders, with party members then choosing the winner.
The online vote will end on 31 October, with the result announced two days later on 2 November, three days before the US presidential election.