Schonfeld, who was 88, died after complications from Alzheimer's disease, the New York Times reported.
Schonfeld launched CNN with Turner in 1980, becoming chief executive of one of the first all-news cable TV networks to provide Americans with round-the-clock coverage.
Under Schonfeld, CNN launched its Crossfire show, in which hosts Pat Buchanan and Tom Braden conducted political debate from the perspective of both the left and the right sides of issues.
The Newark-born TV journalist, who was formally trained as a lawyer, also started News 12, the first 24-hour local news channel on Long Island, New York. He also started the Food Network - another cable TV network - in the early 1990s.
Years before teaming up with Turner, Schonfeld ran an independent news company that provided news footage to local news stations.
It was because of Schonfeld's new judgement and Turner's know-how of satellite television that CNN came into being.
It was also when the US Federal Communications Commission reduced regulations, leading to many independent businesses starting cable news networks.Reuters was not able to contact a representative of Schonfeld or his family for comment.