Becker told Campaign she was already working on the business, which will not compete with VCCP but is relevant to the ad industry,
She resigned last week by prior agreement with VCCP Group chief executive Adrian Coleman.
A VCCP spokeswoman confirmed her departure and said that the day-to-day running of VCCP Media was now in the hands of its chief operating officer Tara Marus, chief integration officer Peter Bennett and joint chief strategy officers Marie Oldham and Simon Jenkins.
Coleman said: "Catherine has made an enormous contribution to the growth of the agency and I wish her all the best in her new venture."
Becker, who has completed her earn-out from the 2015 sale of AdConnection, said she was not yet ready to reveal more about her new venture.
The purchase of AdConnection helped VCCP treble its media billings to about £50m and was followed in 2017 by VCCP Media’s absorption of sister agency Pure Media, which was headed by Marus.