Good Relations was hired earlier this year following a pitch process in December involving several agencies.
Good Relations director Neil Bayley told PRWeek the UK brief would be primarily corporate, but may involve some consumer activity in the future.
Thomas Cook worked with Finsbury until September 2016 on a brief focused on financial comms. Finsbury also handled crisis comms in the aftermath of criticism directed at the company in 2015 over the way it handled the death of two children in Corfu nine years earlier.
Good Relations' appointment follows major changes in the group's communications structure.
Last year Thomas Cook merged its UK and group PR operations under group comms director Alice Macandrew, who joined from Sky in 2015. Recent appointments have included Robin Tozer, also from Sky, as group head of corporate comms, and rival TUI's Alexandra Phillips as group head of internal comms.
Speaking to PRWeek last year, Macandrew said the new hires would form part of a single external comms team, superseding the previous structure with its split between UK and group comms.
In 2016, Thomas Cook brought in Freud Communications on a campaign to mark its 175th anniversary. Macandrew told PRWeek that Thomas Cook "has no other major agency relationship".
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