Clive Lewis has joined the race to replace Jeremy Corbyn as the next Labour party leader.
Speaking to the Guardian newspaper, the Norwich South MP said he wanted to "win back the trust" of voters and "unleash" the Labour movement to win its first general election since 2005.
He said: "The truth is that while making a clear break with the New Labour era in terms of policy and personnel, the party was never able to communicate this to voters in our heartlands.
"When trying to persuade them of our radicalism and sincerity, we often had the legacy of the 2000s thrown back in our faces.
"Persuading voters that we understand the sources of their long-held resentment and frustration, of their disappointment in how Labour has conducted itself since the 1990s, will be the first step towards winning back their trust."
Emily Thornberry confirmed on Wednesday she would also be standing for the top job.
Other potential candidates include Keir Starmer, the shadow Brexit secretary, Rebecca Long-Bailey and Lisa Nandy.
Mr Corbyn announced he would not lead Labour into another election, following last week's result.