Bartsch joins the agency from Rapier, where he held the position of business director, working on accounts including Lloyds TSB and the Department for Business Innovation and Skills.
At JWT, Bartsch will be responsible for developing the agency's CRM capabilities, reporting directly to the chief executive, Guy Hayward, who has attempted to build JWT's digital and direct marketing capabilities since joining the agency 18 months ago.
Hayward said: "As part of our integrated offering, we're reinforcing our CRM capability. Marius comes to us with a good track record and a wealth of knowledge."
At the beginning of 2010, WPP merged its RMG Connect direct marketing offering into JWT, bringing the two companies under the same bottom line with a combined global management.