Foster and Partners, working for Cambridge-based Feilden + Mawson, will transform London's Middlesex Guildhall into the UK's first Supreme Court.
Their redesign and refurbishment of JS Gibson's Grade II*-listed building on Parliament Square will see it transformed by late 2008 into the home of the highest court in the land.
Partner Hugh Feilden said he was delighted to have picked up the job. 'This is just fantastic news for us, ' he told the AJ. 'This is a great building and the work we do will be very important.
Feilden said the firm had decided on Foster because of the practice's commission to redesign Parliament Square. 'We perceived that we would have to properly redo the entrance to remove the references to Middlesex.
'Since Foster is already working on the square it made sense to bring them in early on, ' he added.
Middlesex Guildhall's existing Crown Court work will be relocated elsewhere in London, and plans have been proposed to ensure there will be no adverse effect on the criminal justice system as a result of these changes.
Secretary of state for constitutional affairs and lord chancellor Lord Falconer said he was delighted with the appointment.
'We have assembled an absolutely first-class team to see through the development of what is destined to become one of this country's landmark buildings, ' he said.
'All those involved have track records of excellence. Their brief is to come up with a building design in keeping with the architectural heritage of the area, but to the highest modern standards.
'By 2008 we should have a Supreme Court of which we can all be proud - open and accessible to all, with excellent accommodation for judges and support staff alike, ' he added.