Koch got his start in the film industry as second assistant director to Sydney Pollack on "This Property Is Condemned" (1966) before assisting horror maven William Castle, including serving as dialogue coach on "Rosemary's Baby" (1968). Koch acted as assistant director on some 20 films, beginning with "The April Fools" directed by Stuart Rosenberg (1969). Among the directors he apprenticed with were Sydney Pollack ("The Way We Were", 1973), Roman Polanski ("Chinatown", 1974) and John Schlesinger ("Marathon Man", 1976).
But it is as a producer and executive producer that Koch has made his mark. His first credit was "The Other Side of Midnight" (1977), and he has gone on to produce dozens of successful films with various companies. As president of Rastar Films, he supervised such films as "Peggy Sue Got Married", "Nothing in Common" (both 1986) and "The Secret of My Success" (1987). With Gene Kirkwood, he produced "The Idolmaker" (1980) and "Gorky Park" (1983). Koch was briefly president of production at De Laurentiis Entertainment Group before forming The Koch Company in 1989.
Koch had worked with Paramount since his very first film, and produced several projects there including the Oscar-nominated "Heaven Can Wait" (1978) and "Some Kind of Hero" (1982) before signing a first-look multi-year deal with that studio to produce films (some under The Koch Company banner and some simply through Paramount) in 1991. His first film under that agreement was the football comedy "Necessary Roughness" (1991), and he has since acted as executive producer on the hugely successful "Wayne's World" (1992) and its 1993 sequel, as well as "The Temp" (1993), the Sharon Stone thriller "Sliver" (1993), "Losing Isaiah" and "Virtuosity" (both 1995), and the Richard Gere courtroom drama "Primal Fear" (1996). In the year 2000, he acted as producer to the Ed Norton comedy "Keeping the Faith", (credited as Hawk Koch).