Fitzgerald will reprise his role as Sonny Shine, a children's entertainer who has a dark past. Also elevated to series regular is Bryce Lorenzo, who will again play Hailey Hansen.
Oscar nominee Ann-Margret, whose numerous film credits include State Fair and Bye Bye Birdie, will also be seen in the second season of the series, based on the graphic novel by Grant Morrison and Darick Robertson. She'll have a recurring role as former stage and screen siren Bebe Debarge.
The breakout comedy stars Christopher Meloni as a formerly corrupt policeman turned hitman whose life is changed by an imaginary blue-winged horse.
Fitzgerald also received Tony nominations for his performances in Young Frankenstein and Finian's Rainbow.