Langdon's departure followed a brief meeting in New York on Tuesday with the agency's worldwide chairman and chief executive, John Dooner. McCann later issued a release stating that Langdon had resigned.
Although it is unclear why Langdon was forced out, the situation is complicated by the fact that he had, in recent months, been meeting with Active Value about its proposed bid for Cordiant, and had been touted as its prospective chief executive.
Langdon's position as the head of McCann EMEA had been destabilised by the reinstatement of the former Interpublic chairman and chief executive, Dooner. Dooner replaced Jim Heekin who was ousted earlier this year. Insiders say Langdon and Dooner did not enjoy an easy working relationship.
Langdon will not be directly replaced. David Warden, the regional director of operations for EMEA, and Alistair Cooke, the chief financial officer for EMEA, will take temporary charge of the network's European division.
The position of the UK chief executive (and Langdon appointment) Chris Hunton is now looking uncertain. Suspicions that Dooner is looking to parachute one of his own men into the London office were exacerbated by the IPG release, in which Dooner said: "As relates to the leadership of McCann in London, the agency's clients are currently well served, but we will look to supplement that management team with the appropriate talent in due course."