(written from a Production point of view)
He is perhaps best known for his role as Tim Cavanaugh in the 1982 comedy Porky's and in its 1983 sequel, Porky's II: The Next Day. Both films co-starred Star Trek: The Next Generation guest actor Wyatt Knight, who has since become O'Reilly's best friend. The first Porky's also starred Kim Cattrall. The first two Porky's films also starred Star Trek: The Next Generation guest star Nancy Parsons.
Prior to Porky's, O'Reilly appeared in another popular comedy – 1980's Airplane!, which also featured fellow Star Trek alumni Jonathan Banks and Gregory Itzin, Kenneth Tobey, and Jason Wingreen. Later film credits include Navy SEALs (1990, with Titus Welliver), Philadelphia Experiment II (1993, co-starring Larry Cedar, Gerrit Graham, and Marjean Holden), The Cool Surface (1994, with Teri Hatcher and Matt McCoy), The Unspeakable (1996, with Athena Massey), Carnosaur 3: Primal Species (1996, with Stephen Lee), Eruption (1997, with F. Murray Abraham), Midnight Blue (1997, with Dean Stockwell), and Black Dog (1998).
For television, he has appeared in a number of movies along with fellow Trek performers, including 1981's Splendor in the Glass (with Merritt Butrick, K Callan, and Graham Jarvis), 1987's Carly's Web (with Daphne Ashbrook, K Callan, and Gregory Itzin), 1988's Baja Oklahoma (with Alice Krige and Anthony Zerbe), 1993's A Place to Be Loved (with Sam Anderson and Elizabeth Dennehy), and 2001's Windfall (with Gregg Henry, Jeff Kober, Jeremy Roberts, Daniel Roebuck, and Ray Wise). He also had a role in the epic 1986 mini-series On Wings of Eagles, as did Jim Metzler, Lawrence Pressman, and Diane Salinger.
For episode television, he has made several appearances on Murder, She Wrote, during which he co-starred with John Arndt, Fionnula Flanagan, Dakin Matthews, Andrew Robinson, Mark Rolston, David Ogden Stiers, and William Windom. In 2003, he would appear along with Tim de Zarn, Fionnula Flannagan, and W. Morgan Sheppard. Aside from these roles, he has appeared with David Graf and David Ogden Stiers on M*A*S*H, with Ed Begley, Jr., Ronny Cox, Norman Lloyd, France Nuyen, Jennifer Savidge, Alfre Woodard, and Jane Wyatt on St. Elsewhere, with Harvey Jason and Madlyn Rhue on Houston Knights, with Andreas Katsulas on Hunter, with Michael Ensign and Bruce Gray on Matlock, with Brian Keith on The Commish, with Noble Willingham on Walker, Texas Ranger, with Alan Oppenheimer on Touched by an Angel, with Ed Lauter on ER, and with Katy Boyer and George D. Wallace on The X-Files.