Raised in Jersey City, New Jersey, he graduated with honors from New York's American Academy of Dramatic Arts in 1969. He also trained at the HB Studio in New York, with william Hickey and Michael Becket, and at The Actors Studio with Lee Strasberg.

He is probably best known for his role as Lieutenant Boomer on the original Battlestar Galactica television series. Later, in the 1980 spin-off Galactica 1980, his character was promoted to Colonel, and had moved up in the chain of command to become the Executive Officer of the Galactica.

Jefferson also appeared as a guest star in the pilot episodes of both the 1982 TV series Knight Rider as Muntzy, an undercover police officer and partner of Michael Long (who becomes Michael Knight), and the 1984 pilot of the TV series Airwolf, as the Commander of the aircraft carrier USS Enterprise.

His notable feature film credits include the award-winning Ron Howard film Apollo 13 (1995), where he played a news reporter, and the Wolfgang Petersen film Outbreak (1995) as a Doctor. He also appeared in two films starring football legend Jim Brown, Black Gunn (1972), as his brother, The Slams (1973), as his cell mate, and "Roger Corman"'s "Private Duty Nurses" (1971), as Activist Dr. Elton Sanders , which marked his feature film debut.

In 2015 he appeared in the cameo role of "Admiral Grant (Ben) Satterlee" in the pilot of the web-based series "Star Trek: Renegades" (the pilot episode was developed for television, but was rejected, and subsequently made available on the Internet). In 2007 he portrayed "Captain Gault", a freedom fighter, in the Internet mini series Star Trek: Of Gods and Men, from the same independent production company.