Brian Terkelsen, a senior Madison Avenue executive who had a significant hand in guiding some of the media-buying operations of Publicis Groupe, has resigned from his post, according to a spokesman.

Terkelsen, a veteran who during his time at Publicis’ Mediavest was involved in securing ad support for such developments as the launch of TV’s CW network, has worked for marketers including Procter & Gamble and Coca-Cola. He was an early partner to Mark Burnett, helping him launch “Eco-Challenge,” a precursor to some of the producer’s reality-competition content. He also had a hand in developing a TV concept known as a “showmerical,” or a series of TV ads that told a story across multiple commercial breaks in a single program.

“I have been humbled and honored to lead this agency over the past years, first in the U.S. and most recently globally,” Terkelsen said in a statement. “I’m incredibly proud of the team and the brilliant work we have created in partnership with our clients and I look forward to their bright future.”

Terkelsen had ascended to global brand president for Medivest Spark, one of the nation’s largest media buying firms. Prior to that, he was CEO of Mediavest’s U.S. operations. Before joining Mediavest  in 2003, he spent six years as general manager of Be Here Technologies, overseeing the sales, marketing and production groups and the sale of broadcast services to “Entertainment Tonight,” NBC, the National Basketball Association, the 2002 Winter Olympics and HBO Sports. Before that, he was group general manager of Quokka Sports, where he negotiated programming deals in the adventure and sailing space. He began his career as an investment banker.

Publicis Groupe last year reorganized its sundry media holdings, which also include Starcom, Zenith and Blue 449, once known as Optimedia, in a desire to become more competitive with rivals as digital media gains more emphaiss andafter a series of account losses at Mediavest became cause for concern. Terkelsen at the time was promoted to the global role, but he joins a number of other senior executives at the company who have departed in recent months. The spokesman said said Terkelsen’s depature was not related to account lossses, and noted Mediavest Spark has notched account wins like KFC and USAA in recent months

Publicis Media did not name an immediate successor for Terkelsen, but the spokesman suggested it would seek a new executive for the role. Terkelsen’s next plans could not be immediately learned.