The Greens stand out from Labour and the Liberal Democrats by being the "principled" pro-EU immigration party, according to Jonathan Bartley.
The co-leader's claim to IBTimes UK comes as Westminster faces a realignment in the wake of the Brexit vote.
"We do have a commitment to freedom of movement, very much so, and it's different from the Liberal Democrat position, which is primarily about single-market access, it's different from [Jeremy] Corbyn's position and it's certainly different to the Conservative position," he said.
"We want to work where there's common ground, with other parties, but our position is pretty clear and it's pretty principled."
Bartley, who alongside Caroline Lucas succeeded Natalie Bennett as party leader last September, also said that the Greens are committed to extending Europe's free movement area in the "long-term".
"We are realistic about it, but our long-term policy is to open borders, absolutely. But we are also pragmatic and realistic [about the] climate, but what we're focused on is maintaining free movement," he added.
"For us it's an issue of social justice, we're an internationalist party, we're outward facing."
Bartley's comments come just two days after Corbyn's controversial speech on Brexit. The Labour leader said he his party was "not wedded" to the EU's free movement rules, while failing to provide a substantial policy on the area.
The remarks opened up Labour's left and right flanks to rival parties, with the Greens, Liberal Democrats, Ukip and Conservativesall attacking Corbyn.
Jonathan Bartley: Fact file
Previous post: Former work and pensions spokesman
Hobbies: Drummer and backing vocalist for blues band The Mustangs
Education: Studied social policy at the London School of Economics
But the Greens, who want a second referendum on the terms of a Brexit, risk turning into a left-wing pressure group as the Liberal Democrats become the party of Remain.
"It isn't just about representing the 48%, but also the 52%, healing a lot of divisions that have happened," Bartley said.
"Some people in my family voted to Leave, families were split, the country was split. But it's also about recognising what the EU referendum laid bare and that is a divided country, a country where the big parties have pandered to Ukip with a far-right narrative that is now coming home to roost in terms of a huge rise in hate crimes."
Setting the agenda on the left
The co-leader also argued that the Greens have reinvigorated the idea of a so called "progressive alliance" after deciding not to contest the Richmond Park by-election.
The vote saw former Conservative MP Zac Goldsmith lose the West London seat to the Liberal Democrats' Saray Olney. Labour's Christian Wolmar won just 3.6% of the vote, losing his deposit.
"Post-Richmond, everyone went 'wow, this thing can actually work, this thing can actually happen'," Bartley said.
But the call for a progressive alliance has been shot down by Labour's Shadow Chancellor John McDonnell, while Liberal Democrat leader Tim Farron failed to rule out another coalition with the Conservatives when grilled by IBTimes UK.
Elsewhere, Bartley stressed that the Greens have been able to set the agenda on the left. He pointed to Corbyn's new 20:1 maximum pay ratio policy – the Greens having called for a maximum pay ratio of 10:1 in August 2015.
But for the Greens, who have just one MP after winning 3.8% of the vote at the 2015 general election, is it just about setting the agenda? "We want electoral success, but we also want to change agendas," Bartley said.