Edward Staite joins the agency's lobbying practice after seven years in a number of policy and communications roles with the Tories.
Staite's most recent role at Conservative Party HQ was head of regional media.
Before that he was official spokesman for shadow chancellor George Osborne for two years.
Earlier this year he was seconded to work for Boris Johnson as communications adviser during Johnson's successful London Mayoral campaign.
In the new role, Staite reports to George Hutchinson, chair of Burson Marsteller's lobbying arm.