Harriet Harman has said Labour will be "united" and "fortified" by new leader Ed Miliband, following a week of "roller coaster" emotion.
Closing the party's annual conference, deputy leader Ms Harman said losing the general election was "hard" but there was now a "fierce team" running Labour.
It follows a week when David Miliband quit front-bench politics after his brother Ed beat him to the leadership.
Ms Harman paid tribute to David Miliband as a "towering figure".
He lost the leadership election by just over 1% on Saturday and was the focus of media attention before announcing on Wednesday that he would return to the back benches, rather than serve in Ed's shadow cabinet.
During her closing speech, which is traditionally a light-hearted affair designed to rally party morale, Ms Harman paid tribute to a series of senior Labour figures who are leaving the front bench.
She also praised Ed Miliband, telling delegates: "We will all be united in support of him."
In the first Labour gathering since the party's general election defeat, Ms Harman said she was "disappointed to be in opposition, but proud of what we achieved in government".
She added: "This has been a historic conference. It's been a roller coaster of emotions."
Ms Harman cracked a series of jokes - suggesting she had come out as "most fanciable MP" in Sky News' own version of the Top Trumps car game because her husband - former union worker, now MP, Jack Dromey - had used "the Unite block vote".
She added that Labour was now a "powerful mix of youth and experience", saying: "Some of us are the Facebook generation - some of us are the facelift generation. But together we make a fierce team."
Ms Harman told delegates in Manchester that Labour was "sobered by the scale of the challenge that lies ahead" but "fortified" by the determination of the new leader.
The conference finished in traditional fashion - with members singing the Red Flag and Jerusalem.
Asked in a BBC interview earlier whether Labour's top team would be weaker without David Miliband, Ms Harman replied: "Not at all, but you could tell that there was going to be a focus all the time on trying to find divisions and distinctions between David and Ed.
She said the attention given to David Miliband's "throwaway remark" to her during his brother's conference speech on Tuesday showed the excessive attention he would have faced, had he remained on Labour's front bench.
David Miliband was recorded asked Ms Harman why she was applauding Ed's comment that the war in Iraq was wrong - even though she voted in favour of it. The exchange received widespread media coverage.
Ms Harman, currently shadow Commons leader, declined to say what job she would like in Ed Miliband's first shadow cabinet - which her deputy leader's role means she is a member of by right.
She added that she wanted to play a "big role" in Labour's future but added: "The question of what department is allocated to which member of the shadow cabinet is a matter for Ed Miliband".
Ed Miliband won the leadership contest despite coming second among Labour members, MPs and MEPs, after receiving the most votes among union members taking part in the ballot.
Gordon Brown's former press spokesman Charlie Whelan, who is standing down as political director of the Unite union which backed Ed Miliband, denied working to undermine David Miliband's campaign.
He said: "People think that I had something to do with that... [but] what happened was tens of thousands of night workers, nurses, BBC workers even, voted in the electoral college and voted for Ed Miliband."
In an interview with Channel 4 News, Ed Miliband gave his strongest signal yet that he would put up taxes "for example, taking more from banks or tackling tax avoidance" to protect public services from spending cuts.
Mr Miliband said he would raise taxes - by more than former chancellor Alistair Darling had planned in the previous Labour government - to help pay off Britain's deficit.
Some 49 Labour MPs have put their names forward for the shadow cabinet elections. The candidate, including a host of former ministers and several without ministerial experience, are competing for 19 seats around the table.
Rosie Winterton was elected unopposed as opposition chief whip after Mr Miliband asked incumbent Nick Brown - a close ally of former prime minister Gordon Brown - not to stand.