The agency confirmed that Fallon left his London-based role for the global agency in early October but declined to comment further.
His departure came around the time that Instinctif announced it had hired former Edelman global energy sector chair Rishi Bhattacharya to the role of managing partner in its international corporate affairs practice.
Fallon joined Instinctif under its previous name College Group in September 2013 as managing partner in the global corporate practice. He held his most recent position for 16 months.
He had joined College Group from Hill+Knowlton Strategies, where he was managing director. His earlier roles have included head of group public affairs at the retailer Sainsbury’s and the same role at Heathrow Airport owner BAA.
Fallon also spent time as a researcher and special adviser at the UK Labour Party.