Replacing Nick Bailey, the EMEA chief creative officer, Gill will join on 1 June and report to Steven Moy, Isobar UK’s chief executive.
Gill will work alongside Susanne Jones, the managing director, Patricia McDonald, the chief strategy officer, and Matt Gee, the head of digital transformation.
At DigitasLBi since 2006, when it was known as LBi, Gill has worked on brands such as Apple, Cathay Pacific, E.ON, Honda and Mattel.
Bailey became the EMEA chief creative officer in November last year as Moy was promoted from chief commerce officer at Isobar US.
Moy said: "Simon is a world-class creative with expertise in experience design."