On April 9, the show drew 7.4 million viewers (its season-to-date average), which Nick said was basic cable's most-watched show for that week.
The series is executive produced by Dan Schneider, who is also behind emerging Nick sensation "Victorious," another live-action program.
The iCarly announcement comes as Nick negotiates with advertisers in the kids' upfront market.
In "iCarly," the Web series is sort of a maypole, but the characters also grapple with problems that are challenging to all tweens. The series has a companion iCarly.com Web site and has specials attached.
Carly (Miranda Cosgrove) lives in Seattle with her older brother and guardian, providing a twist on family dynamics. Her father is stationed on a military submarine.
The hit show debuted in 2007.