Green branched out to begin writing, producing and directing documentaries. He received two 1968/69 Emmy nominations for producing and co-writing the "National Geographic" special "Reptiles and Amphibians" and was again nominated for a 1969/70 Emmy as producer of "The Mystery of Animal Behavior" (also for "National Geographic"). In addition, Green worked on "The Amazon", "Birds", several Jacques Cousteau specials, and the Nazi-hunter documentary "Search for Vengeance". Green's feature non-fiction films included the uneven music outing "Spree" (1967, as director), his Oscar-winning look at insects, "The Hellstrom Chronicle" (1971, as producer, director and co-cinematographer), and "The Secret Life of Plants" (1978, as director and co-screenwriter).
His first fictional outing, as screenwriter with Sam Peckinpah for "The Wild Bunch" (1969), earned Green an Oscar nod. But big-screen follow-ups were disappointing. He scripted William Friedkin's "Sorcerer" (1977), a disappointing remake of 1952's "The Wages of Fear", and reteamed with the director for "The Brink's Job" (1978). Green co-wrote "The Border" (1981) for his friend Jack Nicholson and worked on the script for the unsuccessful teen sci-fi drama "Solarbabies" (1986). He spent more than a decade developing "Crusoe" (1988), a revisionist version of the Defoe classic. The final film, on which he shared screenwriting credit, featured a strong leading performance from Aidan Quinn, but it opened to a mixed reception. Green also co-scripted "Robocop 2" (1990) and Charles Russell's hit thriller "Eraser" (1996). He also appeared in the tribute short "The Wild Bunch: An Album Montage" (1996).
Probably Green's biggest successes, though, have been on the small screen. Since the 1980s, he has been associated with three of the more acclaimed cop shows on TV: "Hill Street Blues" (NBC, 1981-1987), on which he served as a coordinating producer and director, "Law & Order" (NBC, from 1992-1994), as writer and co-executive producer, and "NYPD Blue" (ABC, from 1993-1996) as creative consultant. He also co-wrote the TV-movies "Strange New World" (ABC, 1975) and "Three of a Kind" (ABC, 1989), and solo-scripted the biographical miniseries "Robert Kennedy and His Times" (CBS, 1985).