The 34-year-old actor and 43-year-old Mad Men star were announced with Chris Pine and Kristen Wiig on Wednesday. Original stars Amy Poehler, Bradley Cooper, Paul Rudd, Janeane Garofalo, David Hyde Pierce, Michael Showalter and more were confirmed earlier this week.
Wet Hot American Summer debuted as a David Wain-directed movie in 2001. The eight-episode limited television series will serve as a prequel to the film, and follow the counselors on the first day at Camp Firewood. Wain will return to direct, and co-wrote the program with Showalter.
Schwartzman last appeared with Adam Scott in The Overnight, and is scheduled for new Bob Byington movie 7 Chinese Brothers. Hamm will reprise Don Draper on a final season of the AMC drama Mad Men beginning April 5.
Pine will star with Margot Robbie in Z for Zachariah, and reprise James T. Kirk in Star Trek 3. Wiig was announced this week for Ghostbusters III, and is also scheduled for heist film Masterminds and Ridley Scott sci-fi drama The Martian.