The agency has also been charged with helping to support the opening of two new restaurants at Somerset House.
Tom's Terrace at Somerset House opens this month and replaces the River Terrace Café, a summer-only terrace restaurant overlooking the River Thames.
Tom's Kitchen at Somerset House will open at the end of June and will mirror the concept and cuisine of the Tom's Kitchen in Chelsea.
Mason Williams will aim to build the profile of the two eateries across all print, broadcast and online media via a strategic media relations campaign and high-profile launch events.
Compass Group business director Sarah Miller said: ‘The London dining market is increasingly competitive so it was essential that we appointed an agency that had a clear understanding of the challenges we face. Mason Williams will aim to engage proactively with each target audience, from critics to food bloggers and the wider consumer."
Mason Williams won the account after a competitive pitch and it will be headed up by joint managing directors John Williams and Rita Rowe.
As well as expanding his stable of restaurants in London, Tom Aikens is currently appearing as the star of Channel 4's new series Iron Chef.