To mark the poster launch Natalie Bennett, the party leader for England and Wales, met up with parliamentary candidate Caroline Lucas in Brighton.
Ms Bennett warned voters "the time for half measures is over" and urged people to "vote for what you believe in".
She said a Green vote would ensure big firms and rich individuals would pay their "fair share".
Ms Lucas, who became the UK's first Green MP when she was elected in 2010, added: "We have a bold message that will resonate with the people of Brighton and Hove, and across the country.
"Only the Green Party is willing to stand up to the establishment parties on issues like climate change, a resilient economy and protecting the NHS."
The Green Party has vowed to put up the top rate of tax to 60p in the pound, which Ms Bennett said would bring in an extra £2bn a year for public services while acting as a disincentive to firms paying "excessively high salaries".
She added that her party wanted to call for a review of all "commercial animal racing", saying there were animal protection issues which needed to be addressed.
Main pledges
Policy guide: Where the parties stand
"We should be spending our money on public services that meet our essential needs, we should be spending our money on building council homes, homes for social rent.
"We need to invest in renewable energy, energy conservation, there is a whole range of things we need to do to make British society fit for the 21st century," she said.
The Greens have also proposed a "wealth tax" which would be 2% a year levied on people with assets of more than £3m which, Ms Bennett has claimed, could bring in £25bn a year "by the end of the Parliament".
Later, Brian May, the lead guitarist of the rock band Queen, is expected to join Ms Lucas in Brighton to talk about democracy and the importance of voting.
A full list of candidates for Brighton Pavilion can be found here.
Subscribe to the BBC Election 2015 newsletter to get a round-up of the day's campaign news sent to your inbox every weekday afternoon.

Lucio Barani was said to have gestured in the direction of Barbara Lezzi from the opposition Five Star Movement (M5S) on Friday.
Vincenzo D'Anna is thought to have repeated the gesture.
Female senators from various parties responded, demanding that Mr Barani apologise.
The Senate speaker suspended Friday's debate on Italy's constitutional reform bill in the subsequent pandemonium.
The two centre-right senators insisted their actions were misunderstood, but were nonetheless suspended by the speaker's council on Monday.
The speaker said the incidents were "so serious they offended persons and senators, and undermined the credibility of the institutions," news agency Ansa reported.
M5S Senator Alberto Airola was also suspended for a day for insulting members of government.

The incident happened as the 33-year-old walked under a railway bridge on Dumbarton Road, near the junction with Cable Depot Road, at about 22:00 on Saturday 10 September.
Both boys were described as being white, aged about 14 or 15 and wearing dark-coloured sportswear.
One of them had brown hair in a quiff.
The woman was taken to the Queen Elizabeth University Hospital for treatment and later reported the incident to police.
Det Sgt Kevin Mulvenna, of Police Scotland, said: "This was a completely unprovoked and senseless attack on this woman, which has left her blind in one eye. The youths responsible must be caught as soon as possible.
"To point a laser pen at someone is highly irresponsible. Extensive inquiries are ongoing to trace the two boys, with officers carrying out inquiries in the local area and studying CCTV footage to identify them."
He asked anyone with information to contact police.
The Green Party has launched a national billboard campaign urging people to "vote big, vote brave".
[NEXT_CONCEPT]
Two Italian senators have been suspended for five days after allegedly making obscene gestures at female colleagues during a senate debate.
[NEXT_CONCEPT]
Police are searching for two teenage boys after one of them shone a laser into a woman's eye in Clydebank, leaving her blind in one eye.