Herring's departure is linked to his close involvement with Euro RSCG's GLA account, which the agency has failed to develop significantly in recent months.
The executive creative director, Mark Wnek, confirmed the agency was "reviewing its relationship with the business".
Herring's involvement with the account began in 1999 when as a joint creative director at the then Mustoe Merriman Herring Levy, he took charge of a campaign for the London mayor hopeful Ken Livingstone. He took the account with him to Euro RSCG when he left MML the following year, but said he had no intention of doing the same this time.
Although it has continued to work on the main account and other projects, Euro RSCG lost out in last year's controversial creative pitch to promote Transport for London's £5 congestion charge against BMP DDB and the winner, TBWA\London. TfL's corporate account was awarded to M&C Saatchi earlier in the year.
"The timing for my departure has worked out well for all of us," Herring said. "I am anxious to pursue other interests."
Herring was hired by Euro RSCG in January 2000 as a deputy creative director and was promoted to joint creative director alongside his art director partner, Andy McKay, who joined from Lowe the year before as the head of art.
McKay left the agency last year to join Abbott Mead Vickers BBDO.
Herring's departure is the fourth senior creative exit from Euro RSCG in the past two years.
Before McKay left, the former creative director, Paul Shearer, left in July 2000 to work on Nike at Wieden & Kennedy Amsterdam.
The creative director and former Cave Anholt Jonason founder, Jaokim Jonason, who was hired in July 2001 to work on the Citroen account, was made redundant.
Jonason left soon after the £40m Citroen account was lost to Partners BDDH at the beginning of this year.
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