Her replacement is David Whitely, who was promoted to the role from his previous position as campaign content manager. The two had worked together for 18 months.
Gatwick Airport said Baranowski was a strategic lead in the political campaign that is attempting to secure approval to build a new runway at the airport.
As director of LCA, Baranowski will provide strategic advice to existing clients, as well as working on new business opportunities in the transport and infrastructure sector.
LCA, which involves a mix of public relations and public affairs specialising in London issues, was ranked number 12 in PRWeek’s latest list of the top public sector consultancies.
Baranowski said: "I have known LCA for years and have always been impressed by the team, their track record and the client base. It was my first choice when considering an agency."