He will report to global publisher Rhona Murphy, who said: "John has deep relationships in the industry and a wide knowledge of pan-regional business.
"He has proven himself to be an effective and enthusiastic leader through both good and challenging times, always keenly supporting his team members and the Newsweek brand."
Pentin has been regional advertising director of Newsweek since 2005, managing the German, Africa, Eastern Europe and Middle East regions. He had previously held the role of UK sales director.
He joined the London office of the publisher as a sales executive in 1991, after previously holding roles at The Sunday Times and Redwood.In August 2010, The Washington Post Company sold Newsweek to 91-year-old billionaire Sidney Harman, a philanthropist who made his fortune selling audio equipment.