The imminent departure leaves a void at the top of Carat's direct marketing division and comes just two months after Carat's head of direct, David Beale, jumped ship to Aegis stablemate Vizeum.
A Carat spokesman confirmed Halliwell is currently working out his notice, but added that a recruitment drive to appoint a new head of direct is well under way.
Carat decided it can better handle direct clients through the distinct division of Carat Direct 20 months ago, after having rolled it into the rest of the agency as part of a wider restructure in 2006.
The agency is one of the UK’s largest operators in the direct space, sitting alongside Mindshare and MediaCom to service accounts with annual billings worth more than £50m.
The direct division was hit hard by the loss of the Dell account at the start of the year, but continues to service a number of large clients, including Alliance & Leicester and Littlewood’s Shop Direct Group.
Halliwell joined the Aegis agency in July 2005 and was promoted to its board in January 2008. During his tenure he has been responsible for developing its integrated planning solutions.
Prior to joining Carat, he was at direct response specialist Wavv Rapp Collins for five years, working his way up to the position of associate director. He started his career working client-side for three years as a marketing executive at national insurer Axa.