Doust co-founded Inferno 18 years ago with Frazer Gibney, chief executive at FCB Inferno.
The agency was acquired by Interpublic Group at the end of 2013 and merged it with DraftFCB in 2014. Doust’s earn-out came to an end in December 2017.
He leaves the agency on 6 April and told Campaign that he will be staying in the industry but was unable to reveal details.
Doust added: "It feels like a natural time to go. The future is really exciting, the market has been changing rapidly and FCB Inferno is well set to deal with that. For me, helping others and doing other things within a similar sphere will bring interesting challenges."
Gibney’s remit will extend to building a European base in London for the network’s EMEA offices.
FCB Inferno has also hired Nigel Fyfe, group financial director at Publicis UK, as chief operating and financial officer.