He was born in Wapakoneta, Ohio, on August 5, 1930. He received a Bachelor of Science degree in aeronautical engineering from Purdue University and a Master of Science degree from the University of Southern California.

He was selected as an astronaut by NASA in 1962. On March 16, 1966, Armstrong and Dave Scott were launched in Gemini 8 to conduct the first linkup in space, docking with an Agena target satellite. The linkup was successful, but after a short time, the astronauts reported their craft was spinning out of control. They disengaged from the Agena, but the tumbling continued. One of 16 Gemini jet thrusters was stuck open and was spewing fuel into space, imparting the roll motion. Unable to stop the spinning with the main thrusters the astronauts activated a second set of 16 jets intended for use on reentry and after 30 minutes stabilized the spacecraft. Mission Control ordered Armstrong and Scott to cut the flight short and splashed down in a contingency recovery area in the western Pacific. Missed was a planned space walk by Scott.

On July 16, 1969, Apollo 11 astronauts Armstrong, Buzz Aldrin, and Mike Collins departed for the moon. Four days later, Armstrong and Aldrin landed their Lunar Module in the moon's Sea of Tranquility. Armstrong, and then Aldrin, stepped onto the surface and became the first humans to leave their footprints in the lunar dust. They explored the surface and gathered moon rocks for over two hours. The next day they fired off the surface and rejoined Collins in the orbiting mother ship.

Armstrong left NASA in 1971 and became a professor of aeronautical engineering at the University of Cincinnati, where he taught until 1981. He has since been in the business world and he currently is chairman of CTA, Inc.