Gascoigne (pictured) will report to Grayling chairman Richard Jukes and joins the agency’s senior advisory board, where he will service clients across the agency’s public affairs, corporate and consumer divisions.
He arrives from the Foreign and Commonwealth Office, where he worked as a special adviser to then Foreign Secretary Johnson.
Prior to this, Gascoigne worked with Johnson during his time as Mayor of London. He has also worked for the Conservative Party and on campaigns including the London Mayoralty and the 2015 General Election.
Alan Boyd-Hall, head of Grayling Public Affairs, said: "Ben’s arrival represents a significant moment for Grayling, and in particular the company’s public affairs offering.
"Businesses are looking for political guidance and expertise more so than ever, meaning that Ben’s experience of working at the very heart of Westminster and British politics will be invaluable. His political knowledge and insight makes him an excellent addition to the public affairs team, and we are delighted to have him on board."
Gascoigne said: "Grayling is going through a significant period of growth. With its vast network of international and country-wide offices, I am incredibly excited to join the already strong public affairs team and share my experience from the frontline of local and national politics with clients and colleagues.
"Regardless of what is happening in Westminster, this is a period of change and it’s hugely important to try to translate the landscape, whilst providing wider advice to companies in the UK."