He appeared as Claus Van Zandt in 1985 on the soap opera Days of Our Lives, and as Leo Mitchell in 1989 on Santa Barbara. He has also made guest appearances on many other TV series, including Battlestar Galactica (original series), V, Babylon 5, Queen of Swords, and MacGyver. De Longis provided his voice in a Star Trek video game. De Longis was the voice actor as the main antagonist Lord Zygon in Starchaser: The Legend of Orin on 1985 film.
De Longis' best known film role was as the character Blade in the 1987 film Masters of the Universe, in which he was also Frank Langella's stunt double. He also portrayed Gary Ketchum in Road House, performing featured fights against Patrick Swayze's Dalton.
In 1999, De Longis formed Palpable Hit Productions, a production company specializing in bladed weapons and bullwhip training videos. The initial productions presented swordplay for performance, but in 2002 branched out to include historically correct combative fencing techniques in conjunction with the Martinez Academy of Arms.
A very experienced swordsman, he is also known for his roles on Highlander: The Series, as Lymon Kurlow in the third-season episode "Blackmail", and as Ottavio Consone in the fifth-season episode "Duende". De longis auditioned and was considered for the lead role in the series. A martial Artist and weapon master in several disciplines, he played a swordsman opposite Jet Li in the 2006 martial arts epic Fearless, and gave Harrison Ford extensive whip training for the 2008 film Indiana Jones and the Kingdom of the Crystal Skull. He also taught Michelle Pfeiffer how to use the bullwhip for her role as Catwoman in the 1992 film Batman Returns.
In 2009, De Longis appeared on an episode of the Deadliest Warrior as an expert for the weapons and tactics used by william Wallace.
De Longis provided the voice of Marshal Leigh Johnson in the 2010 western video game, Red Dead Redemption. He also appeared in the downloadable content pack Red Dead Redemption: Undead Nightmare.