The agency has been handed a year-long brief to look after consumer and B2B work following a pitch.
Initial activity will focus on driving sales, positioning the ‘best value’ message of the brand, and supporting the work to drive awareness of recent investment in central London hotels.
Siren Communications will target both consumers and trade via a mix of media relations, partnerships and on- and offline tactics.
Thistle, which previously worked with The Red Consultancy, has 31 hotels across the country, with ten in central London.
The team will be led by Siren Communications' consumer director Victoria Savill, who will report to Thistle’s group head of PR, Chris King.
Savill said: ‘We are eager to create some strong results to support sales and make Thistle stand out among the competitive hotel and hospitality market.’