His 50-minute long speech did not mention any Labour leadership contenders but warned of the consequences of being seen as a “party of protest”.
The intervention was widely viewed as a warning to Labour members about the party’s chances at the general election if it elects the left wing frontrunner Jeremy Corbyn.
Polls released on Sunday suggest Mr Corbyn is considered the candidate most likely to worsen Labour’s prospects of winning the next election.
Speaking for the first time on Labour’s leadership race, Mr Brown said the party must learn from its history that only by being elected has it been able to implement Labour policies.
He acknowledged the party was “grieving” after its general election defeat, but said: “There is one thing worse than having broken hearts, it is powerlessness.
“Our hearts can be broken and yet it is worse to find out we are powerless to do anything about it. To see a wrong and not be able to right it, to see an injustice and not be able to correct it, to see suffering and be able to do nothing about it, to see pain and know you cannot heal it, to see good that needs to be done and change that needs to be made and not to be in a position to do it.
‘Lessons of history’
“When I know, and I argued, and I think you believe, that the only way that we can avert the pain and end the suffering is by securing in the future the election of a Labour government to deliver on our priorities.
“And when I see the opinion polls that say the one grouping in the party that is likely to get most votes is the one grouping that even its own supporters say is least likely to be able to form a government, then we have to look at the lessons of our history.”
Voting in the leadership contest opened Friday, with the process closing on September 10th. The four candidates are Jeremy Corbyn, Yvette Cooper, Liz Kendall and Andy Burnham. The new leader will be announced on September 12th.