Green councillors will talk to the Labour Party about working together on Brighton and Hove City Council.
It comes after Labour won 20 seats and the Greens won 19 in the local elections earlier this month. The Conservatives won just 14 seats, and there was one independent councillor elected.
Read more: Labour and Greens could form ‘progressive alliance’ in Brighton and Hove
Labour leader Daniel Yates described the two parties as having manifestos that were “separated at birth”.
He said the Labour team hopes to develop a “shared policy platform” with the 19 Green councillors while finding a way to work together to govern the city.
The Greens have since met to discuss the proposal and said they were willing to talk to Labour.
A statement from the Green Group said: "We thank the city for electing so many new Green voices and we welcome the invitation from Labour to discuss how we can work together to make a difference for our residents. Yet political parties are not the only voices. To achieve truly transformative politics, we also need to take the conversation about how to tackle these issues back to our communities.
"Greens pledge to residents in our city that we will work with all partners - from the Labour Party, to our community groups, voluntary sector and local businesses - to deliver urgent action on critical issues; especially our climate crisis, housing and homelessness and austerity.
"We would welcome the opportunity to work with Labour councillors to set up our shared vision of a citizen's assembly on the climate crisis. We are also keen to explore a City Climate and Biodiversity Crises Summit. We believe now is the time for cross-party action on housing and homelessness. In the face of national uncertainty from a disastrous Brexit, all parties must jointly uphold our status as a city of sanctuary and welcome.
"Over the next four years we will work with the Labour council to achieve what is best for our city. We will never fail to challenge on behalf of our residents, and we will also present new ideas and hold Labour to account when scrutiny is needed. We pledge to stand up for what is best for our city; and to continue to hold our council to the high standards our city expects and deserves."
Councillor Phélim Mac Cafferty, convenor of the Greens, said: "I am thrilled to unveil our promise to the city today that shows our commitment to doing politics differently and working collaboratively on the issues that residents have regularly told us are their highest concerns.
"Having discussed this with our party membership, we will bring our pledge into discussions with the Labour Group of Councillors over the coming weeks offering a new kind of politics for the residents of Brighton and Hove".