The shadow business secretary also vowed to “shake up” the way government works, and put power into the hands of voters, as she bids to replace Jeremy Corbyn.
Described as a “continuity Corbyn” candidate said to be favoured by the current leadership and backed by campaign group Momentum, supporters have bridled at the description.
As she took to the stage for the launch at the Museum of Science and Industry in Manchester, some of the 300 or so supporters at the event broke into a chant of “Oh Jeremy Corbyn”.
Mrs Long-Bailey told them: “Hey guys, were going to have to think of a new song you know. No pressure.”
She was asked why Labour had failed to win voters, returning their worst electoral result since 1935.
Mrs Long-Bailey said: “I think for me we had some fantastic policies, I know because I helped write some of them, and really the message didn’t resonate with our voters.
“And what we should have been talking about is aspiration.
“Because everything we are trying to build and I am going to try to build as leader of the Labour Party is about realising the potential, truly realising that quality of life increase, whether you are a business, whether you are an industry or an individual, our role as a party is to improve your living standards and the wealth you can accumulate as communities.
“And we didn’t say that. We didn’t match that with a message of aspiration.
“We want an economy where everyone does well.”
She also spoke about a trip to Amsterdam she had made before entering politics, being asked “Did you inhale?”
To laughter and cheers from the largely young audience at the event, Mrs Long-Bailey replied: “I’ll leave it up to you to decide why I went to Amsterdam, for flower markets or to partake in local delicacies.”
She added that the country needed a “national discussion” on the “war on drugs”, and to address what she said was the under-funding of police services.
In her speech, Mrs Long-Bailey promised to end the “gentlemen’s club of politics” by devolving power out of Westminster – while promising to introduce a “Green New Deal” that unites Labour heartlands.
She said: “The story of the last few years is that many people feel there is something wrong with their laws being drafted hundreds of miles away by a distant and largely unaccountable bureaucratic elite in Brussels.
“But I’ll be honest, Westminster didn’t feel much closer, and it still doesn’t today.
“That’s why I want to shake up the way Government works and deliver a clear message to voters: we will put power where it belongs – in your hands.”
Mrs Long-Bailey also vowed to root out anti-Semitism in the Labour Party.
She was introduced at the event by newly elected Coventry MP Zarah Sultana, who has apologised about alleged anti-Semitic and anti-Israel comments, attributed to her before she entered Parliament – reportedly saying she would “celebrate” the deaths of Tony Blair and Benjamin Nentanayu, and told someone who was pro-Israel to “jump off a cliff”.
Mrs Long-Bailey added: “We didn’t tackle it properly, we didn’t act quickly enough. I won’t ever let that happen again.”
All the Labour leadership candidates are taking part in the first hustings event in Liverpool on Saturday.