Gerety's early TV work included a bit role in PBS' "The Adams Chronicles" and in several Trinity productions filmed for public television. By the 1980s, he began appearing in higher-profile projects, such as the "The Demon Murder Case" (NBC, 1983), filmed in Newport, RI, the Emmy-winning miniseries "Concealed Enemies" (PBS, 1986) and "Return to Lonesome Dove" (CBS, 1993). Gerety fared well on stage co-starring alongside Judd Hirsch in the Broadway play "Conversations with My Father" in 1982 and won raves for his comic turn as the servant Launce in the New York Shakespeare Festival's "Two Gentleman of Verona" in 1994.
After making his feature debut as a biker in "Complex World" (1991, lensed in Providence), the actor played George in "Wolf" (1994) and Father Brian in "Mrs. Winterbourne", Marcel in "Surviving Picasso" and a lawyer in Barry Levinson's "Sleepers" (all 1996). He began developing his TV cop chic as Sergeant Matt Nelson in the CBS movie "Cagney & Lacy: The Return" (1994) and landed a regular role as the bufoonish Lieutenant Neil Fogarty in the CBS sitcom "Public Morals" (1996), which aired only one episode. His trial run as Internal Affairs Detective Stuart Gharty. during the 1995-96 season on "Homicide: Life on the Street" (NBC) prefaced his joining the talented ensemble of that series as a regular for the 1997-98 season.