The shadow foreign secretary received a standing ovation as he spoke to delegates.
He told them he was “honoured and humbled” by their support but believed if one runs for something, they have to be reconciled to losing
“I’m really, really, really proud. I’m so proud of my campaign, I’m so proud of my party but above all I’m incredibly proud of my brother,” he said.
“Ed is a special person to me. Now he is a special person to you and our job is to make him a special person for all the British people.”
The rest of Mr Miliband’s speech focused on foreign policy and Afghanistan and the Middle East in particular.
He finished by insisting Labour’s “fightback has begun” and hugged his brother before leaving the stage.
Arriving at the venue, he said he would not discuss his next career move until the conference is “well and truly done”.
“This is not a conference about me, it’s a conference about Ed’s leadership of the party,” he told Sky News.
Asked why it was taking so long for him to say whether he would serve in the shadow cabinet, he replied: “I arrived here on Saturday planning a slightly different week.”
Mr Miliband, the favourite at the start of the campaign in May, was beaten by Ed Miliband by 1.3% of the vote.
Since the result was announced, he has faced mounting speculation over whether he will join his brother’s team.
Labour MPs vote on who should join the shadow cabinet and the leader decides which role they get. Nominations opened on Sunday and at least 46 MPs have confirmed they will stand.
The shadow foreign secretary would have to declare this week if he intends to be a candidate.
Ed Miliband said his brother had shown “graciousness” since losing the contest on Saturday.
“He will make his own decisions,” he added.
The older Miliband brother spent Sunday evening mingling with delegates in Manchester.
Accompanied by his wife, Louise, he said: “We have had a really nice day together. (I) haven’t had to spend my time working on speeches or anything else.”
Ed Miliband has said he had had a “brief chat” with his brother on Saturday, but that he did not know if he wanted to remain in politics.
“He needs time to think about the contribution he can make,” he said.
“I think he can make a very big contribution to British politics.
“He needs the space to do that and we’ve got shadow cabinet elections next week, after this conference, so there is a bit of time for all that.”
Other members of the shadow cabinet insisted the close nature of the contest would not damage party unity.
Deputy leader Harriet Harman rejected suggestions Ed Miliband’s victory could renew divisions in the party, saying many people she met during the campaign said they could not decide between the Miliband brothers.
“The idea that there is a complete polarity and that there is sectarianism in the party is an absolute non-starter,” she said.
Current shadow chancellor Alistair Darling will also make a speech at the conference today. – Skynews