Jefferies was born in Lebanon, Pennsylvania.His father was chief engineer at a power plant in Virginia. He had a younger brother named John who worked with him as his chief draftsman. He served in Europe in World War II, was inside of B-17, B-24, B-25 bombers and had four years as a flight test engineer. He had three brothers, John, Richard and Philip, the latter two of whom would become production designers.
He was a member of the Aviation Space Writers' Association and one of the original members of the American Aviation Historical Society. Jefferies restored and flew period airplanes as a hobby. He owned a Waco YOC aircraft and stored it at Santa Paula Airport , California for many years. His Waco, NC17740, c/n 4279, built 1935, is now owned by the Virginia Aeronautical Historical Society and is displayed at the Virginia Aviation Museum, Richmond, Virginia.
Besides creating interiors and exterior of the Enterprise, Jefferies was responsible for designing props (including phasers), sets, the Klingon logo and D-7 battle cruiser. Years later, his concept sketches were revisited and used to design the Starship Enterprise, the Olympic class U.S.S. Pasteur, the Daedalus-class and pre-Federation Vulcan ships.
Contrary to popular belief, Jefferies did not create Star Trek's original shuttlecraft design: although Jefferies submitted his own concept, it was too complex to build with the show's shoestring budget. Gene Winfield's much simpler design was used instead, and Jefferies designed only its interior.
Jefferies had a very pragmatic design ethic: reasoning that a starship's engines would be extremely powerful and potentially dangerous, he positioned them far away from the ship, with the added benefit of modular design so that they could be ejected quickly in an emergency. Figuring that whatever could go wrong would, he put all of the ship's workings on the interior for easy access, eliminating the need for spacewalking in case of exterior repairs. The bridge panels were given an ergonomic design for comfort and ease of use. He was opposed to the idea of PADDs, as well as the goose-neck viewers that appeared in the first pilot. Moreover, he disliked the idea of a large engine room because by his reckoning the entire ship could be run by a single panel on the bridge. Later, Jefferies' work on the bridge of the Enterprise influenced the design of the U.S. Navy master communications center at the Naval Base San Diego.
When Jefferies saw Star Trek: The Motion Picture he fell asleep. He never watched subsequent incarnations of Star Trek, remarking that they had turned his Navy-esque bridge into "the lobby of the Hilton."
Within the Star Trek universe, Jefferies tubes and Captain Jefferies, designer of the NX-class starships, are named in his honor. According to Jefferies, the Enterprise was Starfleet's 17th starship design and it was the first in the series, therefore the ship had the number "1701". This story is documented in one of his sketches.
In June 2003, Jefferies was the guest of honor at the presentation of a documentary about him prepared for the special edition of the Star Trek Generations DVD. Jefferies died the following month in Los Angeles of congestive heart failure.
Jefferies died July 21, 2003 in Los Angeles of congestive heart failure. He was survived by his wife, Mary Ann Jefferies, and his brothers John and Richard. His brother Philip died in 1987.Bombers B-52 (1957)
The Old Man and the Sea (1958)
Wreck of the Mary Deare (1959)
The Untouchables (1959)
Never So Few (1959)
Ben Casey (1961)
Mission: Impossible (1966)
Star Trek: The Original Series (Set Designer; later Art Director) (1966–1969)
Love, American Style (1969)
Weekend of Terror (1970)
Little House on the Prairie (1974)
The Loneliest Runner (1976)
Star Trek: Phase II (1977; never aired, inspiration for Star Trek: The Motion Picture two years later)
Killing Stone (1978)