The SDLP is to stand aside in the Westminster seat in North Belfast for the first time in history to help the pro-Remain cause.
It is one of three constituencies it will not fight – alongside East Belfast and North Down.
Defending its decision, SDLP deputy leader Nichola Mallon said the ambition “must be to return as many pro-Remain MPs who will take their seats and vote to stop Brexit”.
She said that meant “removing pro-Brexit, pro-Boris DUP MPs where possible”.
Mallon added the party “must also seek to weaken those who have cast the interests of Northern Ireland aside for five minutes of influence with a Tory government that has been bad for our communities”.
The move would benefit Sinn Féin in North Belfast, the Alliance Party in East Belfast and independent Sylvia Hermon if she stands again in North Down.
It follows news that Sinn Féin plans to stand in just seven seats – six of which it already has sitting MPs.