Ms Bennett argued there was a “powerful” case for Greens to back continued membership of the EU because of the protection it offers for the environment and workers’ rights.
But she also warned of the dangers of the EU referendum dominating politics for the next four months.
The Greens enjoyed a surge in membership last year and if Ms Bennett’s call is heeded it could add more than 60,000 foot soldiers to the ‘remain’ campaign.
Europe has previously provoked mixed views in the green movement with concerns among some that the EU in its current form is too close to the interests of big business.
But speaking at the Green’s spring conference in Harrogate, Ms Bennett separated out the case for reform from whether the UK should be in the EU at all.
She said: “The arguments for remaining in Europe are powerful, they’re sensible, they’re the future … We’re family, we’re citizens on a continent in which we are all – really – in it together, breathing European air, living beside European waters.”
The 900 conference goers were told the Greens for Europe campaign will “be focusing on the positives of Europe – the way in which free movement of people enriches all of our lives, the defence of human rights and peace, the environmental standards, the workers’ rights, the limits on bankers’ bonuses.”
The Greens endured disappointment in last year’s General Election as they failed to add to the single seat held by Caroline Lucas in Brighton.
In their key target seat in Yorkshire, Sheffield Central, the party rose to second place but was still 17,000 votes behind sitting Labour MP Paul Blomfield.
The election of Jeremy Corbyn as Labour leader has also won back some of the disillusioned supporters who had moved to the Greens.
But the party continues to enjoy a presence on Yorkshire councils, such as Kirklees where there are seven Green councillors, and Ms Bennett asked members to rally again for a fresh push in May’s local elections to turn the “surge” in membership into seats.
“For many communities, there’s the opportunity to elect their first Green councillors – the huge appeal of a new broom sweeping through dusty corridors, a challenger asking tough questions, scrutinising. That’s particularly important in those communities that have been ‘one-party states’ – complacent, unchallenged cabinets without ideas, without hope, without initiative. “
Ms Bennett’s intervention on Europe came as former Conservative Party leader Lord Howard declared his support for a ‘leave’ vote in the referendum.
Mr Cameron was once a special adviser to Lord Howard but his one time mentor was dismissive of the reform package on Britain’s EU membership.
He also contradicted the Prime Minister’s assertion that there would be no prospect of fresh negotiations with EU leaders on better membership terms after a ‘leave vote’.
Lord Howard said: “If they were really faced with a British vote to leave they would think again.
“But I could be wrong. And if I’m wrong, it would just mean that they have finally refused to face up to the need for the fundamental and far-reaching reform that David Cameron set out to achieve.
“And if they are not prepared to reform, I think we are better out.”