Born and raised in Chicago, Conrad began his career as a nightclub singer. Through his friendship with fellow actor Nick Adams, he landed a contract with Warner Bros. which led to his first success on "Hawaiian Eye". When that show was canceled in 1963, Conrad briefly resumed his singing career and attempted to cross-over to big screen stardom. Although he acquitted himself as Pretty Boy Floyd (alongside Nick Adams in the title role) in the low-budget programmer "Young Dillinger" (1965), few other big screen offerings followed. Conrad returned to TV and found his signature role as James West. A second attempt at a big screen career with the labor of love "Live a Little, Steal a Lot/Murph the Surf" (1975) failed to impress reviewers and audiences.

Since the early 1970s, Conrad has made several attempts to find a lasting small screen vehicle. With the exception of his turn as real-life Marine Corps flying ace Gregory 'Pappy' Boyington in NBC's "Baa Baa Black Sheep/The Black Sheep Squadron" (1976-78), he has met with limited success. Frequently collaborating with his children (daughter Joan produced several efforts, daughter Nancy had a regular role on "Baa Baa Black Sheep" and sons Christian and Shane have appeared in several series), Conrad nevertheless has remained busy. He earned some critical respect in the title role of "Will, G. Gordon Liddy" (CBS, 1982) and went on to play a number of tough, sometimes brutal characters like "Charley Hannah" (CBS, 1986) and the mountaineer in both "High Mountain Rangers" (CBS, 1988) and its sequel "Jesse Hawkes" (CBS, 1989). More recently, Conrad co-starred with his second wife, actress LaVelda Fann, in "High Sierra Search and Rescue" (NBC, 1995) and returned to the big screen in a small role in the holiday comedy "Jingle All the Way" (1996). With the announcement that Will Smith would play James West in a big screen version of "The Wild Wild West" (lensing 1998), there was speculation that Conrad would make at least a cameo appearance.