A shadow cabinet minister has insisted there is "no virtue in opposition" and warned Labour cannot change any lives without being in government.
Gloria de Piero recalled the legacy of Keir Hardie in creating a political party to represent workers in Parliament as she pressed the need for Labour to return to power.
Doubts have been raised over the possibility of Labour winning in 2020 following the election of Jeremy Corbyn as leader, with Labour figures warning he may turn them into a "party of protest".
Ms de Piero, the shadow minister for young people and voter registration, told the party's conference in Brighton: "We are Labour because we want to change people's lives. But we know we can't change a single life without being in government.
"Conference debates and members' rallies, they energise us and they motivate us, but only by debating with the public and by rallying voters can we change lives.
"Only by winning power locally and nationally can we change lives.
"Keir Hardie died 100 years ago yesterday. His historic legacy was the creation of a political party that sought representation for labour in Parliament. Labour exists to win power, there is no virtue in opposition."
Ms de Piero also poked fun at Prime Minister David Cameron and Labour deputy leader Tom Watson.
She joked: "Lord Ashcroft has taught us a thing or two about the Prime Minister's upbringing.
"It's fair to say David Cameron and I had different starts in life. Apparently he was sipping champagne on Concorde aged 11. My family were on benefits and I ate free school meals - but we did have some things in common.
"Both of us joined youth societies; he joined the Bullingdon Club, I joined Labour Students.
"The Bullingdon Club met at weekends to go shooting. Labour Students met at weekends to campaign in key seats.
"They'd stay up all night at the Tory black and white ball. We'd stay up all night at Labour conference compositing.
"They had some interesting initiation ceremonies, but I had to share a flat with Tom Watson. I don't know who had the worst deal."
Shadow women and equalities minister Kate Green also insisted Labour would "campaign and resist" Government measures that "hold back progress on equality".
She said: "We will toughen up the law on hate crime.
"We will not tolerate the abuse and contempt suffered by those who rely on our welfare state and are stigmatised as scroungers.
"And we will call out the language of division - because we are a united country."
Ms Green also said: "Parliament continues to be an institution designed by men, for men. Securing equal representation at every level in elected office must be Labour's task."
Earlier, a male-dominated panel greeted delegates as the Labour conference started in the main hall.
One female delegate could be heard shouting: "There are six men on that platform and one woman."
The woman continued speaking but her further comments were inaudible due to applause from fellow delegates.