Most recently Harrison had been working as a consultant at Deutsche Bank, supporting its public affairs and corporate relations. Before that she worked at comms consultancy TLG as director of corporate relations.
Harrison spent the four years to 2009 at Blackstone, where she headed comms for Europe and India. The US asset management and financial services giant is one of the world's largest private equity players, buying Travelport, United Biscuits and Hilton Hotels Corporation during Harrison's time there.
Harrison used Merlin while she was at Blackstone and she led the firm through the review of the private equity industry by the Treasury Select Committee and the European Commission.
Paul Downes, chief executive of Merlin, said the agency would benefit from Harrison's 'excellent strategic comms and political background'.
Meanwhile, Finsbury has recruited Merlin associate director Fiona Crosswell to join the agency as an associate.
At Merlin, she primarily worked on mining and natural resources accounts and will work across mining and industrials at Finsbury.