Hadfield will help drive the group's digital development, initially in sport, where he will expand depth of coverage while integrating data and commercial partnerships.
Hadfield was one of the first national newspaper journalists to leave Fleet Street for the internet in 1995.
He launched football website , which ESPN later acquired for $40m (£27m), as well as an education website called , which he sold in 2003.
Hadfield will report to Edward Roussel, digital editor of TMG.
Separately, Tim Rowell has been promoted to digital publisher.
Rowell will lead the development of key channels on , including finance, fashion, motoring, technology and travel.
Last year he led the editorial rollout of the Telegraph's new web publishing system.
Roussel said: "Tim and Greg will play critical roles in helping Telegraph Media Group deliver its 2009 digital strategy. Our goal is to significantly increase the size or our audience and deepen reader engagement.
"Greg has a track record as a top class journalist who is also a tremendous innovator, as his work at the Sunday Times and with soccernet.com shows.
"Tim did an outstanding job of rolling out our new publishing system and his new responsibilities cover some of the most important areas of coverage for TMG.''
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