Steven is not related to actor Robert Culp, despite having the same last name and a similar physical appearance. He graduated from the College of William and Mary and is best known for his recurring roles as CIA agent Clayton Webb on JAG (1997�2004) and Major Hayes on Star Trek: Enterprise (2003�2004). He had the unusual misfortune to have both of those characters killed off in the same week, in the shows' season finales (though Webb turned up very much alive in the subsequent season premiere of JAG). During the year 2004, Steven became the first actor to appear as a recurring character in four television series simultaneously: The West Wing, Star Trek: Enterprise, JAG and ER.

Culp played Robert F. Kennedy in the film Thirteen Days (2000). He had played Kennedy before, in the TV movie Norma Jean & Marilyn (1996).

He also played Commander Martin Madden in Star Trek: Nemesis (2002), a character written to replace William Riker as Enterprise first officer. However due to the film running too long, Culp's scenes (along with other scenes) were cut from the final film, so Madden can now only be seen in the Nemesis DVD deleted scenes.

Other memorable performances include his role as Peter Drummond in the campy made for TV movie How to Make a Monster in which nerdy computer game programmers accidentally give life to a deadly AI. Members of the software company take turns attempting to beat the game in order save their own lives.

He played Rex Van De Kamp, husband of perfectionist Bree Van De Kamp, played by Marcia Cross, on the TV show Desperate Housewives for one season. Once again, his character was killed off at the end of the season. He also played Republican Speaker of the House of Representatives Jeff Haffley on the TV show The West Wing.

Steven won the Celebrity Poker Showdown 7th Season Championship game.

On the morning of January 1, 2006 his half sister Kathryn Harvey along with her husband and two children were brutally murdered in Richmond, Virginia.