Corcoran will move to Brighton-based digital agency Brilliant Noise, where he will be a client partner on accounts that are not yet determined.
He will leave at the end of April, and is moving to work closer to his home.
Corcoran will not be replaced, as his duties will be taken on by Jon Boardman, Isobar’s new managing director who will join from VCCP in May.
Corcoran has been head of account management at Isobar, whose clients include Kellogg, Adidas and Toyota, for a year and four months.
Before this, he was a business director under the agency’s former name of Glue Isobar, running the Nokia Global team as well as The Guardian and Akzo Nobel accounts.
Prior to that he was an account director when the agency was called Glue London, before it was bought by digital network Isobar. Corcoran has also worked for McCann Erickson and Agency.com.
Nick Bailey, the chief executive and executive creative director of Isobar, said: "We thank Tim for his valuable contribution to Isobar's transformation and wish him every success in his new adventure."
Brilliant Noise was set up by Anthony Mayfield, Maddy Wood and Jason Ryan. It has worked for clients such as American Express, EDF and Picturehouse cinemas.
Jon Boardman, previously a partner and group business development director at VCCP, will complete Isobar’s senior management team, alongside Bailey and the chief strategy officer, Patricia McDonald.