Rebecca Long-Bailey has confirmed she is considering running to replace Jeremy Corbyn as leader of the Labour Party with a pledge to champion "progressive patriotism".
The Shadow Business Secretary blamed the party's "compromise solution" on Brexit, as well as a lack of trust among voters, for its crushing defeat at the General Election earlier this month.
Writing in the Guardian, she said Labour's policy on Britain's EU membership "satisfied too few", but insisted the party's policy agenda was popular.
"We didn't lose because of our commitment to scrap universal credit, invest in public services or abolish tuition fees," the Salford and Eccles MP said.
She claimed Labour "can win again" but said the party must first "come together", as she gave her backing to Shadow Education Secretary Angela Rayner for the role of Deputy Leader.
"We are strongest when we stand together as a pluralist Labour family. That is why I'm not only considering standing to be Leader, but also supporting Angela Rayner as Deputy," she wrote.
"Leadership means leading a team, working with every part of our movement and using all our party's talents to fight the Conservatives at every turn and map Labour's route back to power. Millions woke up to a nightmare on December 13. It's our duty to make sure that doesn't happen again."
Ms Long-Bailey is widely viewed to be the favourite among Corbyn supporters, and frequently defended the party's policies on the airwaves during the election campaign.
However, in comments which will be seen as an attempt to differentiate herself from the Labour leader, she wrote: "From ex-miners in Blythe Valley to migrant cleaners in Brixton, from small businesses in Stoke-on-Trent to the self-employed in Salford, we have to unite our communities.
"Britain has a long history of patriotism rooted in working life, built upon unity and pride in the common interests and shared life of everyone.
"To win we must revive this progressive patriotism and solidarity in a form fit for modern Britain."
She also suggested Labour had further to go in giving its members control of the party, writing: "Our promise to democratise society will ring hollow if we can't even democratise our own party."
Despite not having formally declared her candidacy, Ms Long-Bailey is seen as a frontrunner in the contest, with her main rivals expected to include shadow Brexit secretary Sir Keir Starmer and Wigan MP Lisa Nandy.
Shadow foreign secretary Emily Thornberry and shadow Treasury minister Clive Lewis are the only two to have officially declared their candidacy.
Labour Party chairman Ian Lavery is also reportedly considering a bid, with a spokesman telling the Daily Mirror he was "seriously considering all of his options at present".