Koppel agreed to do at least six programs a year for Discovery, and said he expected the first to come in late summer or fall.
It was a coup for the basic cable network, prime-time home of ''American Chopper'' and many hours of programming on sharks, particularly given that Koppel and his executive producer, Tom Bettag, had been talking to HBO about a production deal.
Koppel said it was a more comfortable fit at Discovery, given that HBO was essentially an entertainment network. Discovery also offered more immediate access to airtime if, for example, his team wanted to respond to a story like the West Virginia mining disaster by producing a special on mine safety, he said.
Koppel won't have a news organization behind him like at ABC, but Discovery chief Billy Campbell noted that Discovery Communications distributes BBC America and Koppel would have access to the BBC's material, if necessary.
The longtime ABC News anchor left ''Nightline'' after 25 years in November. The late-night news show he originated has continued on ABC with three new anchors, dumping Koppel's single-topic format for a magazine approach.
Bettag said Koppel's team plans to continue the old ''Nightline'' tradition of exploring topics - crime and punishment, race relations and international news - that have few outlets at other TV news organizations.
With 250 shows a year at ABC, only about 5 percent were truly great, Koppel said.
''Our challenge here at Discovery is to do nothing but the great shows,'' he said. ''Will we succeed at that? I don't know. But that is our goal.''
Koppel said he didn't talk to CNN, Fox News Channel or MSNBC about a job because he couldn't see any of them - like the broadcast networks - agreeing to set aside a night of prime-time programming for a documentary and town hall-style meeting on a topic.
The cable news networks seem preoccupied with ''a desperate race to be first with the obvious,'' he said, and pay more attention to what is recent rather than what is important.