The former Weber Shandwick EMEA chief strategy officer is understood to be pursuing strategic comms consultancy work under his own company with other brands and businesses.
In a statement sent to PRWeek, W Communications founder and CEO Warren Johnson said: "We’d like to thank Adam for is work on behalf of the agency and know that he’ll be a welcome resource for any business looking for a senior strategic mind. We wish him all the best for the future."
In the same statement, Mack said: "I have thoroughly enjoyed my time at W, working with the many very talented people across all levels, and I am proud to have been part of the agency’s recent and continued growth.
"I’m now looking forward to a new chapter in my career with a focus on helping businesses make sense of the bigger issues facing them, the societies they are part of and the environment they impact."
Mack has worked in the agency sector for more than 20 years, starting at Porter Novelli and moving on to senior leadership roles at Freuds and Weber Shandwick, where he built strategic insight and analytics capabilities and helped lead clients as diverse as Unilever, Eurostar, Mars, Sony and Bono’s Project RED.
He previously worked with Johnson at Freuds and was brought on at W Communications in January 2018 "to build the agency’s strategic capability - especially through digital and social - and keep the agency ahead of the curve on such areas as data analytics, ROI measurement and channel strategy".
Day-to-day operations of the agency will still be led by Johnson, managing director Richard Tompkins and deputy managing director Sophie Raine.
W also grew revenue by 26 per cent in 2018 to £8.4m and has reently picked up a swag of new clients, including an expanded brief with Spotify and new contracts with Papa Johns, Trainline.com, KERB and Wiggle.