OCS Group has won a contract worth £87.5m to provide a range of services, including catering, to the Ministry of Justice (MoJ).
The five-year, multi-service deal also includes security, cleaning and concierge, mail room and reprographics services.
It is worth an estimated £17.5m a year, with the option to extend the contract for another two years.
OCS will deliver services across four regions including London and the South East, the South West, Wales and the Midlands.
Within those regions, a total of 30 "clusters" have been awarded to OCS, covering upwards of 200 buildings including the MoJ headquarters and QE11 Conference Centre in Westminster.
Each site has a lead manager and cluster leads dependent on the size and geographical spread of the cluster.
Bob Taylor, chief executive of OCS UK, Ireland and Middle East said: "We pride ourselves on the quality of our public sector offering, and we're thrilled to add such a prestigious Government body to our client base."