The contract, worth an estimated £1m in total turnover, commenced yesterday (1 August) and will run until the end of August 2012.
It is the first time the Imperial War Museum has appointed a sole caterer.
Seasoned will manage both private and corporate evening events at the venue, employing two full-time members of staff onsite in newly created roles.
"As a business we are proud that our talented and creative chefs can deliver great food, whatever the occasion or venue," said Seasoned Events managing director Colin Sayers.
Seasoned Events also holds sole catering contracts at Tower Bridge Walkways and the Royal Courts of Justice.
Click here to and let us know your thoughts.