Sinn Fién will occupy offices in Westminster today after a ban preventing them from using facilities available to MPs was lifted in December.
The party was prevented from using Westminster facilities as its MPs refused to pledge allegiance to the British queen.
The Tories and unionist parties have criticised the decision to provide facilities. Shadow Northern Ireland secretary Mr Quentin Davies called it a "propaganda coup" for republicans.
Sinn Fén has four MPs and will receive three offices. There will be one each for party president Mr Gerry Adams MP and Martin McGuinness MP, and the third will be shared by Mr Pat Doherty and Ms Michelle Gildernew.
The party still pursues a policy of abstentionism and refuses to take up its seats in the Westminster parliament, which it does not recognise as legitimate.