Rebecca Long-Bailey has become the sixth candidate to join the race to become the next Labour leader.
In an article for the Tribune magazine, she said Labour needs a “socialist leader who can work with our movement, rebuild our communities and fight for the policies we believe in”.
She joins Sir Keir Starmer, Emily Thornberry, Clive Lewis, Lisa Nandy and Jess Phillips in the contest.
The result of the contest will be announced on 4 April.
The three-month contest will officially get under way on Tuesday when nominations open and candidates face questions from MPs at the first hustings in Parliament.
Ms Long-Bailey, who has been shadow business secretary since 2016, is believed to have the support of key figures within Jeremy Corbyn’s inner circle, including shadow chancellor John McDonnell.
She also has the backing of shadow education secretary Angela Rayner, who is standing for the deputy leadership.
Confirming her candidacy, the MP for Salford and Eccles said Labour had a “mountain to climb” to get back to power but there was a “path to victory” if the party stayed true to its socialist values.
She said Labour’s election defeat last month, its fourth in a row, was due to a failure of campaign strategy and the “lack of a coherent narrative” rather than a repudiation of its policies.
If elected leader, she said there would be no return to the “Tory lite” agenda which she said had held the party back for many years.
“We need a leader that can be trusted with our socialist agenda,” Ms Long-Bailey said.
“A leader who is totally committed to the policies and has the political backbone to defend them. We need a proud socialist to lead the Labour Party, driven by their principles and an unwavering determination to see democratic socialism in our lifetime.”
Making her pitch for the top job, Ms Long-Bailey said she was “not your typical politician” and could be trusted to “fight the establishment tooth and nail”.
Under the timetable agreed by Labour’s ruling body on Monday, the contenders have until 13 January to show they have the support of the 22 MPs and MEPs required to get on the ballot paper.
They must also demonstrate they have the backing of 5% of local Labour parties and three affiliated bodies – two of which must be trade unions.