The Liberal Democrats have voted overwhelmingly to pledge to scrap council tax at their spring conference in Southport.
Kennedy's speech is likely to be a conference highlight
The party believes its plan to replace council tax with a local income tax will be key to wooing voters at the local and general elections.
Leader Charles Kennedy said there was no doubt the "unfairness" of the council tax was something that needed to be addressed.
Delegates also backed a proposal to allow doctors to assist a terminally ill patient to end his or her life under strict circumstances - but the measure is unlikely to appear in the party's manifesto.
Before the council tax vote Mr Kennedy shook hands with a delegate wearing a Tony Blair face mask and insisted: "I think the message is clear Tony - axe the tax."
He was surrounded by about 60 activists, who braved the wind in front of Southport Theatre and waved yellow banners and fake axes to chant: "Axe the Tax".
Mr Kennedy, who earlier this week missed the Budget statement due to a stomach bug, said unlike the Tories and Labour, the Lib Dems would be fighting the coming elections on a platform to introduce a "fairer" local income tax.
"I think that's going to win a lot of votes come these elections," he said.
The party released research which suggested that up to 2.5m people were paying too much council tax.
It claims some of the poorest people are paying out up to £453 per year too much, and says council tax has risen faster than any other normal household bill since Labour came to power.
'Out of touch'
During the debate, local government spokesman Ed Davey told delegates: "Council tax is unfair - you know it's unfair and I know it's unfair.
"We want it scrapped, not capped and we are winning that argument.
"The fairest alternative to council tax is local income tax, based on the ability to pay."
Retired lecturer Gill Fifield and her husband Tony, a retired company director, said that as Bridport town councillors they had encountered many pensioners struggling to pay the council tax.
"Pensioners are saying they are having to cut essentials to meet the council tax, like going on holiday and running a car, which is a lifeline in a rural area like ours," said Mrs Fifield, 59.
Gloria Cawood, 56, a councillor for Mendip District Council and Somerset County Council, said: "I have a multi-millionaire in my area who pays as much council tax as somebody who is in an ordinary council tax with a fairly low income - that's not fair."
Delegates also backed proposals to allow medically assisted dying. While the proposal will now become party policy, it will still be a matter of conscience for the Lib Dems 54 MPs.
Chairman Matthew Taylor said it was "unlikely" that a policy which allowed MPs a free vote would be included in the party's manifesto.
Mr Kennedy's health is also likely to be an issue, although he has insisted he will be well enough to make his keynote speech on Sunday.