This is a list of notable events, premieres, releases, series cancellations and endings, and other business ventures for Nickelodeon in the year 1999.
- January 17 - The Brothers Flub, an animated series by SunBrow Animation, starts its run on Sunday mornings.
- February 11 - Maisy premieres on Nick Jr., before it was moved to Noggin in 2002.
- May 1 - SpongeBob SquarePants premieres after the Kids' Choice Awards; it would begin regularly airing on July 17th.
- August 16 - Rocket Power premieres in primetime.
- October 16 - 100 Deeds for Eddie McDowd and The Amanda Show debut on an revamped SNICK, entitled SNICK House.
- November 28 - Little Bill premieres in primetime.
- December 31 - ChalkZone premieres its first episode as part of the Nick New Year's block, but the rest of the first season would be delayed to 2002.
- The Off-Beats' Valentines
- The Henry & June Show
- February 20 - Nick GaS ends its run, in preparation for its channel's launch.
- March 27 - Nicktoons TV airs its final broadcast; it would become its own channel in 2002.
- June - Henry & June's Nicktoons Summer Jam debuts, and would continue for the resit of the summer.
- July 7 - Nick Flicks movie block begins.
- September - 101% Whizbang! With Henry and June debuts on weekday afternoons.
- November - U-Pick Fridays
Home video releases
- March 30
- CatDog: Together Forever
- CatDog: CatDog vs. the Greasers
- The Rugrats Movie is released on VHS, Laserdisc, and DVD
- August 3 - Rugrats: Runaway Reptar
- October 1 - Rugrats: Make Room for Dil
Nickelodeon character debuts
- Oh Yeah! Cartoons: Penny Sanchez, Tootie, Jorgen Von Strangle
- SpongeBob SquarePants: SpongeBob SquarePants, Patrick Star, Squidward Tentacles, Mr. Krabs, Sandy Cheeks, Sheldon Plankton, Mermaid Man and Barnacle Boy, Gary the Snail
- Rocket Power: Otto Rocket, Sam Dullard, Twister Rodriguez, Reggie Rocket, Tito Makani, Raymundo Rocket
- The Amanda Show: Penelope Taynt, Crazy Courtney