Martin replaces Matt Bagwell, who left the agency last year to join Conchango.
In his new role, Martin has been briefed to apply his experience in offline advertising and direct marketing to online channels.
Martin resigned from Arc in December following the integration of the creative department with that of its sister ad agency Leo Burnett. He had been at the agency for five years, working his way up to creative director in 2005.
He began his career in New Zealand in 1995 at McCann-Erickson, before moving to the UK in 1999 and joining Arc in 2002 as a senior copywriter.
Gareth Phillips, the managing director of Syzygy, said: "Creative chiefs from digital agencies are moving to traditional agencies. Aaron's appointment is the flipside of this. We wanted big-agency thinking, and he ticks all the boxes: digital, TV, DM, press, poster, radio, experiential."