El Onizuka was born on June 24, 1946, in Kealakekua, Hawaii. He graduated with a Bachelor's degree in Aerospace Engineering from the University of Boulder, Colorado, in June 1969, and with a Master's degree in Aerospace Engineering in December 1969. While at the university he was commissioned a 2d Lieutenant in the U.S. Air Force Reserve through the Air Force ROTC program on June 6, 1969, and then went on active duty beginning on January 15, 1970. His first assignment was as a Flight Test Engineer with the Service Engineering Division, Sacramento Air Logistics Center, at McClellan AFB, California, from January 1970 to July 1974, followed by Test Pilot School at Edwards AFB, California, from August 1974 to July 1975. Capt Onizuka served as a Flight Test Engineer at the Air Force Test Pilot School at Edwards AFB from July 1975 until he was selected as an Astronaut Candidate with NASA in January 1978. He completed Astronaut Training in August 1979, and served as a Space Shuttle Mission Specialist with NASA for the next 6 years. His first spaceflight was as Mission Specialist on the Space Shuttle Discovery (OV-103) during STS-51C, the first Space Shuttle Department of Defense mission, from January 24 to 27, 1985. His final space flight was as Mission Specialist on the Space Shuttle Challenger (OV-099) during STS-51L on January 28, 1986, and was killed when the Space Shuttle Challenger exploded 1 minute and 13 seconds after liftoff from Cape Canaveral, Florida. His remains were recovered from the crew capsule and he was buried at the National Memorial Cemetery of the Pacific in Honolulu, Hawaii. He was posthumously promoted to Colonel and later was awarded the Congressional Space Medal of Honor. Sunnyvale Air Force Station in Sunnyvale, California, was renamed Onizuka Air Force Station in his honor in 1986.

His Meritorious Service Medal Citation reads:

Captain Ellison S. Onizuka distinguished himself in the performance of outstanding service to the United States while assigned to the United States Air Force Test Pilot School, Edwards Air Force Base, California, from 7 July 1975 through 15 January 1978. During this period, Captain Onizuka managed and was responsible for major improvements to the Data Acquisition capabilities of United States Air Force Test Pilot School aircraft and Air Force Flight Test Center General Support Fleet aircraft. His efforts in this area contributed immeasurably to the capability of the Flight Test Center to support the high priority testing of the F-16, F-15, and B-1 and the capability of the Test Pilot School to train Fight Test Pilots and Engineers in modern data acquisition techniques. The exceptional initiative, managerial abilities, and superior degree of professionalism displayed by Captain Onizuka far exceeded the demands of his position. The singularly distinctive accomplishments of Captain Onizuka reflect great credit upon himself and the United States Air Force.