In this new role, Lewis will oversee TMG's digital businesses and set up a new entrepreneurial unit based in Euston, with a team of 50.
He will retain his role as editor-in-chief of The Daily Telegraph, The Sunday Telegraph and Telegraph.co.uk.
Lewis's deputy, Tony Gallagher, has been appointed editor of The Daily Telegraph.
Murdoch MacLennan, chief executive of Telegraph Media Group, said: "For the past three years, [Will] has done a first class job editing The Daily Telegraph while successfully integrating our print and digital editorial operations.
"[He] also orchestrated undoubtedly the biggest story of the decade, our highlighting of the systematic abuse of MPs' expenses.
"I believe now is the time to fast forward to the next stage of our digital transformation. Using the Telegraph's powerful brand and reputation, Will has been charged with building a digital unit designed to capitalise on cutting edge ideas, driving new revenue streams by better serving our customers."
Gallagher has been deputy editor of The Daily Telegraph since September 2007. He was previously executive head of news.
Gallagher and The Sunday Telegraph editor Ian MacGregor will continue to report to Lewis.
Lewis said: "I am very excited by this new opportunity. As editor-in-chief I will continue to supervise the strategy and overall content of our newspapers and website, while working on our digital revenue streams.
"It is a tribute to our chairman, Aidan Barclay, and the Barclay family that they have invested millions of pounds in this exciting venture, which will help us rapidly expand our digital operations."
Benedict Brogan, assistant editor and chief political commentator, has been appointed deputy editor of The Daily Telegraph.
Mark Skipworth remains executive editor, overseeing the Saturday edition. Chris Evans, executive head of news, becomes Gallagher's number three.
