Worth a six-figure sum, the account will include consultancy and ad-hoc projects alongside the four key launches.
Britain’s oldest airline brand, Monarch appointed Tin Man after a competitive four-way pitch.
David Page, the airline's group head of comms, who joined from Freuds in April 2016, said: "Tin Man came in with laser-like focus and creativity. They proposed a spot-on strategic platform that is not only closely aligned to the Monarch brand, but also captures the current zeitgeist and news agenda. This was underpinned with some exceptional creative thinking."
The airline previously worked with Speed Communications, and before that with Big. Both agencies are owned by The Mission. Monarch's corporate PR agency is Bell Pottinger.
Tin Man founder Mandy Sharp said the airline had "a rich heritage, a great story and many happy customers".
Founded in 2013, Tin Man's client list includes ITV, the fundraising site JustGiving, Trainline and Nickelodeon.