The Greens are fielding more than 1,300 candidates at next month's local elections - with "big gains" expected in a number of London boroughs.
Greens say the voting system makes it difficult for smaller parties
Peter Cranie, the party's elections co-ordinator, says he hopes seats will be secured in places like Camden, Islington and Hackney.
"We are also looking to potentially make gains in Manchester, Sheffield and Huddersfield," he said.
More than 4,000 council seats will be decided in the 4 May elections.
"With a total of 70 sitting councillors already and over 1,300 candidates, the Greens are the emerging force in local government," said Mr Cranie.
This is despite the use of the first past the post voting system "that makes representation difficult for smaller political parties", he said.
"We are confident of further gains, particularly in the London boroughs, and are the strongest challengers to Labour and the Liberal Democrats in a number of wards."
The Greens are also targeting councils in Norwich and Oxford where they already hold the balance of power.
The party will officially launch its local election campaign in central London next Tuesday.
Contests will take place in 20 English unitary authorities, 32 London boroughs, 36 metropolitan districts and 88 English shire districts.