In 2003 he won a Taurus World Stunt Award for best fire stunt in Red Dragon and in 2005 he was nominated twice for best work with a vehicle in the films Taxi and The Punisher. In 2007 he was nominated for another Taurus World Stunt Award for best specialty stunt in the comedy film Unaccompanied Minors, alongside Star Trek stunt performers Chrissy Weathersby and Gary Kasper. Johnston was the personal stunt double for actor Bruce Willis in most of his films between 1985 and 1991. He has also doubled for stars such as Billy Wirth, Christian Slater, Vince Vaughn, Adrian Pasdar, and Colin Farrell.
Among his stunt resume are films such as Gotcha! (1985), Blind Date (1987), Die Hard (1988), The Hunt for Red October (1990), Die Hard 2 (1990), The Bonfire of the Vanities (1990), Hook (1991), Batman Returns (1992), Death Becomes Her (1992), Addams Family Values (1993), Speed (1994), Casper (1995), Broken Arrow (1996), Barb Wire (1996), The Lost World: Jurassic Park (1997), Inspector Gadget (1999), The Mexican (2001), K-PAX (2001), Minority Report (2002), xXx (2002), S.W.A.T. (2003), National Treasure (2004), Jarhead (2005), Next (2007), Pirates of the Caribbean: At World's End (2007), Live Free or Die Hard (2007, with Tim Russ and Chris Palermo), There will be Blood (2007), Eagle Eye (2008) and Battle Los Angeles (2011).
He has also performed stunts in television series such as Moonlighting (1985), Alias, Lost and ER.