Ms Bairbre de Brún, one of Northern Ireland's three members of the European Parliament, is to resign her Assembly seat, Sinn Féin confirmed yesterday.
Ms de Brún, who gained the EU seat last June at the SDLP's expense, was minister for health in the power-sharing Executive prior to suspension in October 2002.
Sinn Féin has written to Assembly authorities to give notice of the resignation and to nominate west Belfast councillor Ms Sue Ramsey to fill the vacancy.
Under Assembly procedures, elected members supply a list of replacements should they resign or die while in office. This is to avoid a by-election in a multi-seat, multi-party constituency and to avoid the majority parties gaining seats from smaller parties which have won final seats.
Mr Conor Murphy, leader of the Sinn Féin Assembly group, said last night: "It would be very difficult for any individual to deliver effectively for constituents across the six counties in Europe and simultaneously maintain the sort of local constituency service which Sinn Féin require from our MLAs."
Ms de Brún said among her regrets was that "the opportunity to bed down the political process through the institutions was squandered by the British government at the behest of the leadership of political unionism".
She added: "Direct rule is bad for the six counties. Time and again since the suspension of the political institutions this has become obvious. When allowed to work at all, power sharing, the equality agenda and the all-Ireland institutions worked well."