Seiken, whose 30-year career in journalism includes spells as vice-president of AOL Europe and editor-in-chief of washingtonpost.com, has been responsible for all digital content, products and businesses at PBS for the past six years.
He will be responsible for all aspects of editorial operation across the Telegraph Media Group, with both Tony Gallagher and Ian MacGregor, editors of The Daily Telegraph and Sunday Telegraph respectively, reporting directly to him.
His appointment follows the announcement of a restructure of the group's 550 editorial staff in March that led to the ditching of 80 "mostly print-based" editorial roles and the recruitment of 50 new digitally-focused positions.
Seiken, who starts next month, has been tasked with transforming the Telegraph into a "fully integrated, entrepreneurial multimedia news organisation providing the best English language journalism and content in the world".
Murdoch MacLennan, chief executive of TMG, said: "This appointment is vital to the future of our business and in achieving our ambition to become the foremost English-language multimedia news and content provider. There could not be a better person for this crucial role than Jason Seiken.
"He has a lifetime of experience in the media industry and an extraordinary track record of completing profound business transformations. He is a remarkable leader who is at the cutting edge of global developments in the media, with a pioneering track record of delivering radical, durable change in companies which include some of the world's leading media brands."
Seiken, who has dual UK and US nationality, said: "I am absolutely delighted to be joining Telegraph Media Group at this critical moment in its continuing development. The Telegraph is an iconic global media brand, renowned for its quality and its innovation."