The agency hired Frizell in August 2012 as executive director, media, in charge of its 'connector' team of dedicated media specialists.
Frizell is leaving this week and according to ITV is to take up his position as editor of the weekday afternoon programme in spring.
Earlier in his career he edited GMTV, then the most-watched UK television show, and worked as a correspondent for Reuters, Sky News and ITV.
Matt Neale, president, international, at the agency, said: "I’m very proud one of our people has secured this important editorship and pleased that Martin has agreed to continue his relationship with us by offering media advice to clients. Martin’s move comes as Neil joins as head of social assuming responsibility for our real time marketing product, The Bridge."