Over the coming months, InHouse PR will promote a series of reports that are expected to feed in to the Conservative Party's manifesto for the next general election.
The reports will range from gun and knife crime, to mental health and the criminal justice system.
Policy Exchange is said to have close links to Cameron and some reports have credited the think tank with leading the Conservatives' revival in fortunes. It was set up in 2002 by Nicholas Boles, now Johnson's chief of staff at City Hall, and Michael Gove, now in the shadow cabinet.
Katie Perrior, director of iNHouse PR, said: ‘Policy Exchange are among the leading think tanks informing political debate in the UK at present and we look forward to working with them to push their reports out to a wider audience.'
InHouse PR worked with Johnson for the duration of his London mayoral campaign.