Sir Keir Starmer has confirmed he is standing in the contest to replace Jeremy Corbyn as Labour leader.
The shadow Brexit secretary, seen as a frontrunner in the contest, has written in the Sunday Mirror that Labour needs to “rebuild fast” to restore trust.
The contest was called after Mr Corbyn announced he would stand down as leader after Labour’s heavy election defeat.
Shadow foreign secretary Emily Thornberry and shadow treasury minister Clive Lewis have also confirmed they are standing.
Another candidate seen as a frontrunner in the contest, shadow business secretary Rebecca Long-Bailey, is expected to launch her leadership bid soon.
‘Rebuild and win’
Writing in the Sunday Mirror, Sir Keir said: “We cannot bury our head in the sand: Labour must rebuild and fast. We have to restore trust in our party as a force for change and a force for good.
“The millions of people who needed change at the last election still need change. The moral fight against poverty, inequality and injustice must continue.
“But as we rebuild we must not lose sight of our values or retreat from the radicalism of the past few years.”
Sir Keir, who backed Remain in the EU referendum and was one of the leading figures in the party advocating for a new referendum, will kick off his leadership bid by visiting Brexit-backing Stevenage on Sunday.
Some of Mr Corbyn’s allies have blamed Sir Keir’s Brexit stance for the party’s disastrous election performance last month, where much of its traditional, Leave-backing, Northern strongholds fell to the Conservatives.
Sir Keir said: “Over the coming weeks, I’m looking forward to getting back on the campaign trail and talking to people from across the country about how Labour can rebuild and win.
“Britain desperately needs a Labour government. We need a Labour government that will offer people hope of a better future.
“However, that is only going to happen if Labour listens to people about what needs to change and how we can restore trust in our party as a force for good.”
Sir Keir’s background
The human rights lawyer, who was made Queen’s Counsel in 2002, served as head of the Crown Prosecution Service and accepted a knighthood in 2014, and has struggled to shake-off perceptions of privilege.
He was named after Labour Party founder Keir Hardie and he has emphasised his upbringing by his toolmaker father and nurse mother in London’s Southwark when dismissing allegations he is too middle-class to speak to the party’s historic heartlands.
His CV includes co-founding the renowned Doughty Street Chambers and advising the Policing Board to ensure the Police Service of Northern Ireland complied with human rights laws.
He entered Parliament as the MP for Holborn and St Pancras in 2015.
Critics have also raised concerns that Sir Keir is seen too much as a Londoner.
Sir Keir will appear on the BBC’s political programmes on Sunday, including the Andrew Marr Show.
Under current rules, would-be candidates for both the leader and deputy leader roles must first be nominated by more than 20 MPs.
They must also secure nominations from at least 5% of Labour’s constituency parties or three affiliated bodies – two of which must be trade unions.
A timetable for the leadership election – and any rule changes – is set to be decided by the party’s ruling National Executive Committee (NEC) on Monday.