Green Party leader Natalie Bennett has called for a "peaceful political revolution" at May's election to end the "failed experiment of austerity".
Addressing her party's spring conference, Ms Bennett said the poorest in society had been "blamed for the mistakes of the wealthy".
She called for free social care for the elderly, arguing her party can be "the agents of change".
The Greens have seen a surge in their poll ratings and membership.
But critics say their policies - which include renationalising the railways and giving every adult a £72 a week "citizen's income" - do not add up.
Ms Bennett herself has come in for criticism within her own party after she struggled to explain her party's housing policy in a radio interview last month.
But former leader Caroline Lucas, the party's only MP, praised Ms Bennett's leadership, saying she had done a "fantastic job" in helping the party grow and broaden its appeal.
Speaking in Liverpool, Ms Bennett said that the Green Party of England and Wales could have a "huge say" in the direction of the country after the 7 May election.
"In just nine weeks' time, you will have in your hands something miraculous, the possibility of a peaceful political revolution," she told activists.
"Your vote can change the face of Britain. It can end the failed austerity experiment, end the spiteful blaming of the poor, the sick, the vulnerable for the mistakes of the wealthy.
"This election can be a turning point in history. The moment where we can deliver a better Britain, a Britain which works for all of its people. A Britain which cares."
She called for a living wage and an end to "the scourge of zero hours" which she said was symbolic of "austerity Britain".
"The Green Party is calling time on the politics of low wages, economic insecurity and the fear of the food bank," she said.
In the speech, she called for legislation to roll back private healthcare within the NHS, saying there had been a "rapid and insidious infiltration of the profit motive".
"Free healthcare is the very cornerstone of our NHS. Whether you are rich or poor you have the high quality of service - the best that is available.
"That's something the Green Party will restore - and extend".
She said the Greens' manifesto, due to be published at the end of the month, would contain a pledge to make social care free at the point of delivery for the over 65s.
"We believe that to be a decent, humane, caring society, social care must be free....Social care is not a privilege, it is a right.
She said this would be paid for an increase in taxation on the wealthiest in society, including a wealth tax, a financial transactions tax and an increase in income tax on those earning £100,000 or more.
The Green Party, which currently has one MP, is looking to substantially boost its representation in Parliament amid predictions of another hung Parliament.
Former Green Party leader Caroline Lucas has called on the party to form a "progressive alliance" with the SNP to maximise their influence in the next Parliament, particularly if Labour forms the next government.
"Whether we have one MP or ten we can be a progressive force for good," she said.
Ms Lucas said her victory in Brighton Pavilion in 2010 gave the party "something to defend" and the party's record since then had proved it "could be a force for good without selling our your principles".
The Green Party has been outpolling for Liberal Democrats in some national opinion polls and has seen its membership quadruple to more than 55,000 in the past year.