Lord Kinnock has hailed Ed Miliband's "magnificent" first speech as Labour leader, telling activists: "We've got our party back."
The former Labour leader heaped praise on his successor in an impassioned speech at a Tribune rally at the party's conference in Manchester.
He said Mr Miliband would unify Labour and "set us on a course to earn victory at the next election".
And he laid into the coalition for creating "unjustified panic" over cuts.
Lord Kinnock, who was a prominent supporter of Ed Miliband during the leadership contest, said he had "ignited with truth, with candour, with absolute honesty what we stand for" in his speech to delegates on Tuesday.
And instead of the bitter infighting of the past, there would "no pause for self indulgence," with Labour "on the front foot from the start".
"It was magnificent and I will never be able to praise him enough," the peer told a packed hall.
"A trade union delegate leaned over and said 'Neil, we've got our party back'. I thought that was so accurate as an instantaneous response to the leader's speech."
'Climate of fear'
Ed Miliband used his speech to draw a line under New Labour and declare that a "new generation" was now in charge.
He praised the party's achievements in power, but said it had been "wrong" on the Iraq war and other issues such as bank regulation, immigration and claiming to have abolished "boom and bust".
Lord Kinnock led the party to election defeat in 1987 and 1992 but his modernisation of the party is credited with paving the way for the 1997 New Labour success.
He said Ed Miliband's first task was to oppose the coalition over the way he said it had whipped up public fear over the budget deficit to justify "savage" and "rapid" spending cuts.
He accused the coalition, with the help of the media, of "a deliberate, comprehensively organised effort to generate and rule through a climate of fear" which he said was worse than what he had seen in the Thatcher years.
He said there was no moral, political or economic justification for the "slashing and slicing" of public spending the coalition had planned.
He said the task for Labour members and trade unionists was to "convince our fellow citizens that it is wrong, and it must and can be effectively opposed and diverted so that communities, and lives, and families, and futures, and opportunities, are saved".
"We are not in as grave a situation as the newspapers preach and George Osborne tells us," he argued, pointing to evidence from the bond markets and saying the economy had been in a far worse state before and recovered.
But he also told activists to "box clever" when it came to strike action and "win by securing the breadth of support" from the public rather than staging walkouts.
"Don't get mad, get even and win," he told the rally, organised by left wing magazine Tribune.