Entertainment Weekly reports that Kravitz will play himself in the show and will be a client of Ari Gold (Jeremy Piven).
The programme's creator Doug Ellin explained: "He's got to get Lenny to do a movie so someone else will do something for him."
Meanwhile, Entourage's executive producer Mark Wahlberg will appear alongside P Diddy in a scene set on the golf course.
"Turtle [Jerry Ferrara] is starting a business, and he's trying to get them to invest in it," Ellin said. "He's going to a lot of people about this investment."
Entourage returns for its seventh season on June 27 on HBO, while the episode featuring Kravitz, Diddy and Wahlberg will air in August.
