Mr. McLennan, 40, succeeds Ann Fudge in that role. Last year, Ms. Fudge, former Kraft Foods marketer who joined the agency in 2003, said she planned relinquish day-to-day control of the ad agency following a tough stint that included client losses like Sony's Sony Electronics and Ford Motor Co.'s Jaguar.
Ms. Fudge remains chairman-CEO of Y&R Brands, a WPP Group-owned unit that includes Wunderman and Burson-Marsteller.
The appointment of Mr. McLennan follows a long search. He'll be expected to help turn around the Madison Avenue giant. A release from the agency said that in his previous post he managed more than a dozen companies in the Australia region, quadrupling revenues over the past four years.
Mr. McLennan joined Y&R from George Patterson Bates in 2002 and last year managed the two agencies' merger. He worked at PattersonBates for 17 years, working in every area of the agency. In 1999, he was named national managing director.