The departure comes as the Lorne Michaels-produced series was to have gone back into production this month with a new format. But Applegate has left before the show could resume taping.
“It’s been a great experience working on 'Up All Night,' but the show has taken a different creative direction and I decided it was best for me to move on to other endeavors," said Applegate, who begins filming "Anchorman 2" this month. "Working with Lorne Michaels has been a dream come true and I am grateful he brought me into his TV family. I will miss the cast, producers and crew, and wish them the best always.”
Applegate's exit may be the final blow for the stuggling comedy as NBC decides if it can or should be saved. It faces a series of difficult questions: Should it recast Applegate's role? Write off the mother of a newborn? Or just call it quits?
There was no immediate word from the network Friday.
The comedy has already been dealt a slew of changes, including the exit of creator Emily Spivey. It also increased co-star Maya Rudolph's role before it debuted in fall 2011, in part because of her role in the hit "Bridesmaids."
NBC announced in October that the series would shut down for three months and use that time to convert the show from a single-camera to multi-camera comedy.
It was scheduled to go back into production this month to shoot five new episodes that, for the first time, would have been taped before a live audience.
Other shows — most recently CBS's "Two and a Half Men" — have pressed on after losing lead actors. But most of those shows were hits. "Up All Night" has earned barely passable ratings since debuting last season.
In a Television Critics Association panel last month, NBC entertainment president Jennifer Salke was asked why NBC didn't just junk the show and find a new vehicle for its cast, which also includes Maya Rudolph.
"There’s a lot of thought that went into all of that and conversation with all the talent involved," Salke replied. "That was a show that wasn’t performing the way we needed it to. We are not fools. We know that that talented cast of actors, they’re not growing on trees. They still felt like there were stories to tell in that world and were collectively really passionate about continuing to tell them, as well as Lorne Michaels and that group. So we started looking at the show and thinking what was the best format for it, given that they felt a little tied down by the format they were in and the creative direction of the show."
When NBC announced the format change for "Up All Night" in October, entertainment chairman Bob Greenblatt said the network and Michaels agreed it would "infuse the show with more energy."
Greenblatt noted that both Rudolph and Applegate had recently hosted Michaels' "Saturday Night Live" and "love the reaction from a live audience." He also said he believed the show could "make a seamless tradition to the new format."
He also suggested the change was essential to the show's survival, saying, "this will give us another show to consider for next season in this new format."