Before finding his true vocation, LaGravenese studied acting and experimental theater at New York University. He went on to try his hand on the nightclub circuit as half of a short-lived comedy team. In addition to holding down such jobs as bartender and street vendor, the struggling actor helped make ends meet by writing monologues for other thespians. He segued to films as a co-writer on the mild social comedy "Rude Awakening" (1989).

LaGravenese received extraordinary notices for his adaptation of Robert James Waller's amazingly popular novel, "The Bridges of Madison County". Most reviewers derided the merits of the source material while marveling at the transformation wrought by the screenwriter and by director Clint Eastwood. LaGravenese trimmed much of the literary and philosophical fat away from the tale to create a lean and satisfying love story. He shrewdly shifted the focus to the female character Francesca (Meryl Streep) and humanized her mythic lover Robert Kincaid (Eastwood). The story also benefited from an expanded framing device in which the grown-up children learn of their ostensibly staid mother's brief infidelity many years before. Finally, LaGravenese added some characters to flesh out the story's themes while, at Eastwood's insistence, retaining enough of the original fulsome dialogue to satisfy the novel's fans.

That same year, LaGravenese provided the script for the comedy/drama "Unstrung Heroes". The story of a 12-year-old who runs away to live with his eccentric uncles when his mother takes ill, the film (directed by Diane Keaton) was an intelligent and quiet look at a family in disarray; only the over-the-top performances of some of the cast deflected from the script. He also co-scripted (with Elizabeth Chandler) the critically acclaimed adaptation of Frances Hodgson Burnett's "A Little Princess".