Jarre had been a self-described "Civil War freak" since childhood, when he received toy soldiers from the era for Christmas.
Moved to research the 54th, Jarre read the colonel's letters and two books, Kirstein's "Lay This Laurel" and Peter Burchard's "One Gallant Rush," which became source material for the 1989 film "Glory."
"I never thought I could interest anybody in it," Jarre told The Times in 1990. "A Civil War epic, about black people? But I'd got really attached to the story.... I'd end up in tears when I got through writing."
The script initially engendered controversy and was called racist, partly "because Jarre is white and partly because the language is outspoken and the characterizations not invariably idealized," Charles Champlin, then The Times' arts editor, wrote in 1990.
"Glory," which was directed by Edward Zwick, went on to win three Academy Awards, including one for actor Denzel Washington. The New York Times review praised Jarre's "good, lean screenplay."
His screenplay for 1993's "Tombstone" "was really the first time anyone has tried to present Wyatt Earp in his entirety," Kurt Russell, who portrayed Earp in the movie, told The Times in 1994.
Val Kilmer, who played Doc Holliday in the film, called the script "one of the greatest that he'd ever read," the Portland Oregonian reported in 1996.
Hired to direct "Tombstone," Jarre was removed as director six weeks into filming. His attention to detail "may have paid off in atmospheric detail" but also may have slowed him down as a director, The Times said in 1994.
The western garnered mixed reviews but was a hit at the box office.
"He was a fabulous raconteur," his aunt said, "and knew the history of just about everything."
Jarre was born Aug. 6, 1954, in Detroit and moved to Los Angeles in the early 1960s with his mother, Laura Devon, an actress who made her film debut in "Goodbye Charlie" (1964).
His parents divorced, and for a time he lived with his father in Wyoming.
In the 1960s, Jarre had small acting parts in the TV series "Flipper," which starred Brian Kelly, then married to his mother. She subsequently married Oscar-winning composer Maurice Jarre, who adopted Kevin.
Among Jarre's other writing credits are "Rambo: First Blood Part II" (1985), "The Devil's Own" (1997) and "The Mummy" (1999).
He occasionally produced films and acted. In "Glory," he had a small role as a white soldier who picks a fight. As the regiment heads for battle, he yells, "Give 'em hell, 54th."
Besides his aunt, Jarre is survived by cousins.