Andrews will work alongside Dylan Williams, Mother's strategy director, and oversee a restructure of the 16-strong planning department.
Other key duties will include developing the agency's brand beyond traditional advertising and marketing the agency to clients.
No start date has yet been confirmed, but Andrews is expected to join later this year. He will receive equity in the business under the agency's standard staff policy based on years of service.
As well as advising Mother on how to widen its client offering beyond advertising, Andrews and Williams will restructure the agency's strategic department and could pair senior and junior planners together similarly to creative teams.
Williams said: "Matt brings a wealth of digital and channel thinking, as well as fresh craft skills that we'll benefit from in this second stage of Mother's evolution."