The SDLP and Fianna Fáil have entered an "unprecedented and historic" partnership aimed at restoring public faith in politics.
The announcement was made at a press conference in Belfast on Thursday.
The SDLP announced a series of common policies with Ireland's Fianna Fáil pledging to shake up efforts to resolve the powersharing crisis at Stormont.
They promised a politics which works after more than two years of non-government in Northern Ireland, and moves to unite Ireland's people amid what they see as the threat posed to north/south cooperation by Brexit.
They also said they would prioritise the delivery of public services.
SDLP leader Colum Eastwood said: "Our parties are determined to work together to try and change the failure our politics lies frozen in.
"We will not do so by gestures or gimmicks or through photo opportunities.
"Instead we will do it through a focus on policy and issues, not party or sectarian positioning.
"Both the SDLP and Fianna Fail have agreed to work in partnership on an unprecedented programme of public engagement in Northern Ireland which can help frame an ambitious and practical agenda for the future of this island and our people."
The SDLP have trailed in the polls behind a dominant Sinn Fein in recent years.
Fianna Fáil are in a confidence and supply agreement to support Ireland's minority coalition Government.