Falco's stint on the comedy series will mark her first TV appearance since the "Sopranos" season finale in June. Details about her "30 Rock" character were not released Thursday.
Falco said she's a fan of "30 Rock," which launches its second season at 8:30 p.m. October 4.
"I have laughed out loud at this show, and I am thrilled for the opportunity to work with such great comic actors," she said. "I am very excited."
"30 Rock," which is nominated for 10 Emmys, stars Tina Fey, who also is creator and executive producer, and Alec Baldwin.
"We're thrilled to have such an amazing actress come join us," Fey said, quipping that "also, a lot of guys on our crew want 'The Sopranos' ending explained to them."
Jerry Seinfeld will also guest-star on "30 Rock" this season, while Rip Torn, Will Arnett and Sherri Shepherd will reprise their guest roles.
Falco is up for lead actress in a drama series at the 59th Primetime Emmy Awards, which take place September 16. She has won three Emmys for her role as Carmela Soprano.