Part of a £220 million redevelopment of the hospital site, the Llewelyn Davies scheme includes plans to overhaul two buildings and convert a former clinical block into a new cardiac centre.
The project will form phase two of 'a major reconfiguration' programme which is being backed by the Great Ormond Street Hospital Trust - an organisation largely funded by charitable donation.
Neil Cadenhead, director in charge of health, Llewelyn Davies, said: 'Llewelyn Davies has recently worked for some of the country's most prestigious research and teaching hospitals, including UCLH, Barts and the Royal London and Addenbrooke's.
'We look forward to delivering buildings at Great Ormond Street which will enable the hospital to provide the best possible service to patients.'
The practice has already completed similar masterplanning work for Our Lady's Hospital for Sick Children in Dublin and at Brighton's Royal Alexandra Children's Hospital.