The multi-generational duo, who performed "The Lady is a Tramp" together on Bennett's "Duets II" album, intend to make a jazz album together.
"'Of all things, she called me from New Zealand and said, 'I want to do a jazz album with you,'" Bennett told Rolling Stone. "A lot of people don't know it, but she's a phenomenal jazz singer."
For material, the album will draw on a to-be-announced composer -- one Bennett says deserves more notice.
"I can't mention the composer because I don't want anybody to do it before we do it, but there's a great composer that's very underrated, very famous, but not as famous as Gershwin or Porter," he said. "But he did as many hit songs as anybody, and so we're gonna do a big swinging album."
Bennett's own "Viva Duets" is due Oct. 23, the latest album for the tireless musician. The singer, now 86, says he'll start on the Gaga project "as soon as I can." Gaga herself will return with "ARTPOP" in 2013, an album that will double as a multimedia experience.
"The most major way to fully immerse yourself in 'ARTPOP' is through the app," Gaga said in a statement earlier this month. "'ARTPOP' will be released as an iPad, iPhone, mobile and computer compatible application that is completely interactive with chats, films for every song, extra music, content, Gaga-inspired games, fashion updates, magazines, and more still in the works!"