He will work on strategy across the group’s portfolio and report directly to group marketing and brand director Suzi Williams.
Warren had been taking time away from marketing, most recently working as a broadcast journalist for an English language news channel in France.
He worked in the same brand strategy role at BT for three years before taking the global brand director role at IT consultants Logica in 2010.
He has also held senior roles at the now defunct Central Office of Information and agency side at Wolff Olins and Wieden & Kennedy.
Bowyer left BT in December to join Great Ormond Street Hospital as director of marketing and public fundraising.