Citizen hired Cargill in January from Cheil UK where he had been creative director for two years.
Before Cheil, Cargill worked at Fallon London with consumer brands including Nokia, Eurostar and Asda. He was also creative director at private members club The Hospital Club for six years and previously worked in marketing at Channel 4.
Cargill was brought in to replace Joe Sinclair who resigned from the role last October.
PRWeek understands that Cargill has been dismissed and Citizen is currently interviewing for his replacement.
Ctizen declined to comment while Cargill was unavailable for comment at the time of going to press.