Armstrong was born on August 5, 1930, near Wapakoneta, Ohio.

In 1947, at age 17, Armstrong began studying aeronautical engineering at Purdue University.

Armstrong's call-up from the Navy arrived on January 26, 1949, requiring him to report to Naval Air Station Pensacola in Florida for flight training with class 5-49.

After passing the medical examinations, he became a midshipman on February 24, 1949.

Flight training was conducted in a North American SNJ trainer, in which he soloed on September 9, 1949.

On March 2, 1950, he made his first aircraft carrier landing on the USS Cabot, an achievement he considered comparable to his first solo flight.

On August 16, 1950, Armstrong was informed by letter that he was a fully qualified naval aviator.

Neil's mother and sister attended his graduation ceremony on August 23, 1950.

On November 27, 1950, he was assigned to VF-51, an all-jet squadron, becoming its youngest officer.

Neil made his first flight in a jet, a Grumman F9F Panther, on January 5, 1951.

Neil was promoted to ensign on June 5, 1951, and made his first jet carrier landing on USS Essex two days later.

On June 28, 1951, Essex had set sail for Korea, with VF-51 aboard to act as ground-attack aircraft. VF-51 flew ahead to Naval Air Station Barbers Point in Hawaii, where it conducted fighter-bomber training before rejoining the ship at the end of July.

On August 29, 1951, Armstrong saw action in the Korean War as an escort for a photo reconnaissance plane over Songjin.

Five days later, on September 3, he flew armed reconnaissance over the primary transportation and storage facilities south of the village of Majon-ni, west of Wonsan. An initial report to the commanding officer of Essex said that while attacking a target, Armstrong's F9F Panther was hit by anti-aircraft fire. The report indicated he was trying to regain control and collided with a pole, which sliced off 2 feet (1 m) of the Panther's right wing. Further perversions of the story by different authors added that he was only 20 feet (6 m) from the ground and that 3 feet (1 m) of his wing was sheared off.

Armstrong's regular commission was terminated on February 25, 1952, and he became an ensign in the United States Navy Reserve. On completion of his combat tour with Essex, he was assigned to a transport squadron, VR-32, in May 1952.

Neil was released from active duty on August 23, 1952, but remained in the reserves.

He was promoted to lieutenant (junior grade) on May 9, 1953.

Armstrong graduated with a Bachelor of Science degree in Aeronautical Engineering in January 1955.

Following his graduation from Purdue, Armstrong became an experimental research test pilot. He applied at the National Advisory Committee for Aeronautics (NACA) High-Speed Flight Station at Edwards Air Force Base. NACA had no open positions, and forwarded his application to the Lewis Flight Propulsion Laboratory in Cleveland, where Armstrong made his first test flight on March 1, 1955.

Armstrong's stint at Cleveland lasted only a couple of months before a position at the High-Speed Flight Station became available, and he reported for work there on July 11, 1955.

Armstrong met Janet Elizabeth Shearon, who was majoring in home economics, at a party hosted by Alpha Chi Omega. According to the couple, there was no real courtship, and neither could remember the exact circumstances of their engagement. They were married on January 28, 1956, at the Congregational Church in Wilmette, Illinois.

On March 22, 1956, he was in a Boeing B-29 Superfortress, which was to air-drop a Douglas D-558-2 Skyrocket. He sat in the right-hand pilot seat while the left-hand seat commander, Stan Butchart, flew the B-29. As they climbed to 30,000 feet (9 km), the number-four engine stopped and the propeller began windmilling (rotating freely) in the airstream. Hitting the switch that would stop the propeller's spinning, Butchart found it slowed but then started spinning again, this time even faster than the others; if it spun too fast, it would break apart. Their aircraft needed to hold an airspeed of 210 mph (338 km/h) to launch its Skyrocket payload, and the B-29 could not land with the Skyrocket attached to its belly. Armstrong and Butchart brought the aircraft into a nose-down attitude to increase speed, then launched the Skyrocket. At the instant of launch, the number-four engine propeller disintegrated. Pieces of it damaged the number-three engine and hit the number-two engine. Butchart and Armstrong were forced to shut down the damaged number-three engine, along with the number-one engine, due to the torque it created. They made a slow, circling descent from 30,000 ft (9 km) using only the number-two engine, and landed safely.

His first flight in a rocket-powered aircraft was on August 15, 1957, in the Bell X-1B, to an altitude of 11.4 miles (18.3 km). On landing, the poorly designed nose landing gear failed, as had happened on about a dozen previous flights of the Bell X-1B.

In June 1958, Armstrong was selected for the U.S. Air Force's Man In Space Soonest program, but the Advanced Research Projects Agency (ARPA) canceled its funding on August 1, 1958.

Neil became an employee of the National Aeronautics and Space Administration (NASA) when it was established on October 1, 1958, absorbing NACA.

On November 5, 1958, "Man In Space Soonest" was superseded by Project "Mercury", a civilian project run by NASA.

As a reservist, he continued to fly, with VF-724 at Naval Air Station Glenview in Illinois, and then, after moving to California, with VF-773 at Naval Air Station Los Alamitos. He remained in the reserve for eight years, before resigning his commission on October 21, 1960.

In June 1961, Karen was diagnosed with a malignant tumor of the middle part of her brain stem; X-ray treatment slowed its growth, but her health deteriorated to the point where she could no longer walk or talk. She died of pneumonia, related to her weakened health, on January 28, 1962, aged two.

On March 15, 1962, he was selected by the U.S. Air Force as one of seven pilot-engineers who would fly the X-20 when it got off the design board.

In April 1962, NASA announced that applications were being sought for the second group of NASA astronauts for Project Gemini, a proposed two-man spacecraft. This time, selection was open to qualified civilian test pilots.

On May 21, 1962, Armstrong was involved in the "Nellis Affair". He was sent in an F-104 to inspect Delamar Dry Lake in southern Nevada, again for emergency landings. He misjudged his altitude, and did not realize that the landing gear had not fully extended. As he touched down, the landing gear began to retract; Armstrong applied full power to abort the landing, but the ventral fin and landing gear door struck the ground, damaging the radio and releasing hydraulic fluid. Without radio communication, Armstrong flew south to Nellis Air Force Base, past the control tower, and waggled his wings, the signal for a no-radio approach. The loss of hydraulic fluid caused the tailhook to release, and upon landing, he caught the arresting wire attached to an anchor chain, and dragged the chain along the runway.

At Brooks Air Force Base at the end of June, Armstrong underwent a medical exam that many of the applicants described as painful and at times seemingly pointless.

Armstrong visited the Seattle World's Fair in May 1962, and attended a conference there on space exploration that was co-sponsored by NASA. After he returned from Seattle on June 4, he applied to become an astronaut.

NASA's Director of Flight Crew Operations, Deke Slayton, called Armstrong on September 13, 1962, and asked whether he would be interested in joining the NASA Astronaut Corps as part of what the press dubbed "the New Nine"; without hesitation, Armstrong said yes.

The selections were kept secret until three days later, although newspaper reports had circulated since earlier that year that he would be selected as the "first civilian astronaut".Armstrong was one of two civilian pilots selected for this group; the other was Elliot See, another former naval aviator. NASA announced the selection of the second group at a press conference on September 17, 1962. Compared with the Mercury Seven astronauts, they were younger, and had more impressive academic credentials.

On February 8, 1965, Armstrong and Elliot See were announced as the backup crew for Gemini 5, with Armstrong as commander, supporting the prime crew of Gordon Cooper and Pete Conrad.

The crew assignments for Gemini 8 were announced on September 20, 1965. Under the normal rotation system, the backup crew for one mission became the prime crew for the third mission after, but Slayton designated David Scott as the pilot of Gemini 8. Scott was the first member of the third group of astronauts, whose selection was announced on October 18, 1963, to receive a prime crew assignment.

Gemini 8 launched on March 16, 1966. And Armstrong became the first American civilian in space.

The final assignment for Armstrong in the Gemini program was as the back-up Command Pilot for Gemini 11, announced two days after the landing of Gemini 8. The launch was on September 12, 1966, with Conrad and Gordon on board, who successfully completed the mission objectives, while Armstrong served as a capsule communicator (CAPCOM).

On January 27, 1967, the day of the Apollo 1 fire, Armstrong was in Washington, DC with Cooper, Gordon, Lovell, and Scott Carpenter for the signing of the United Nations Outer Space Treaty. The astronauts chatted with the assembled dignitaries until 18:45, when Carpenter went to the airport, and the others returned to the Georgetown Inn, where they each found messages to phone the Manned Spacecraft Center. During these calls, they learned of the deaths of Gus Grissom, Ed White, and Roger Chaffee in the fire. Armstrong and the group spent the rest of the night drinking scotch and discussing what had happened.

On April 5, 1967, the same day the Apollo 1 investigation released its final report, Armstrong and 17 other astronauts gathered for a meeting with Slayton. The first thing Slayton said was, "The guys who are going to fly the first lunar missions are the guys in this room." According to Cernan, only Armstrong showed no reaction to the statement. To Armstrong it came as no surprise—the room was full of veterans of Project Gemini, the only people who could fly the lunar missions. Slayton talked about the planned missions and named Armstrong to the backup crew for Apollo 9, which at that stage was planned as a medium Earth orbit test of the combined lunar module and command and service module.

The New Apollo Crew assignment was officially announced November 20, 1967.

After Armstrong served as backup commander for Apollo 8, Slayton offered him the post of commander of Apollo 11 on December 23, 1968, as Apollo 8 orbited the Moon.

The crew of Apollo 11 was officially announced on January 9, 1969, as Armstrong, Collins, and Aldrin, with Lovell, Anders, and Fred Haise as the backup crew.

According to Chris Kraft, a March 1969 meeting among Slayton, George Low, Bob Gilruth, and Kraft determined that Armstrong would be the first person on the Moon, in part because NASA management saw him as a person who did not have a large ego.

A press conference on April 14, 1969, gave the design of the LM cabin as the reason for Armstrong's being first; the hatch opened inwards and to the right, making it difficult for the lunar module pilot, on the right-hand side, to exit first.

A Saturn V rocket launched Apollo 11 from Launch Complex 39 site at the Kennedy Space Center on July 16, 1969.

The landing on the surface of the Moon occurred several seconds after 20:17:40 UTC on July 20, 1969.

The flight plan called for a crew rest period before extravehicular activity, but Armstrong requested the EVA be moved to earlier in the evening, Houston time. When he and Aldrin were ready to go outside, Eagle was depressurized, the hatch was opened, and Armstrong made his way down the ladder. At the bottom of the ladder Armstrong said, "I'm going to step off the LM now". He turned and set his left boot on the lunar surface at 02:56 UTC July 21, 1969, then spoke the now-famous words, "That's one small step for man, one giant leap for mankind."

About 19 minutes after Armstrong's first step, Aldrin joined him on the surface, becoming the second human to walk on the Moon. They began their tasks of investigating how easily a person could operate on the lunar surface. Armstrong unveiled a plaque commemorating the flight, and with Aldrin, planted the flag of the United States.

After they re-entered the LM, the hatch was closed and sealed. While preparing for the liftoff from the lunar surface, Armstrong and Aldrin discovered that, in their bulky space suits, they had broken the ignition switch for the ascent engine; using part of a pen, they pushed the circuit breaker in to activate the launch sequence. The Eagle then continued to its rendezvous in lunar orbit, where it docked with Columbia, the command and service module. The three astronauts returned to Earth and splashed down in the Pacific Ocean, to be picked up by the USS Hornet.

In 1970 he completed his Master of Science degree in Aerospace Engineering at the University of Southern California (USC).

Armstrong and his first wife, Janet, separated in 1990, and divorced in 1994, after 38 years of marriage.

He met his second wife, Carol Held Knight, at a golf tournament in 1992, when they were seated together at breakfast. She said little to Armstrong, but two weeks later he called her to ask what she was doing. She replied that she was cutting down a cherry tree, and 35 minutes later Armstrong was at her house to help. They were married in Ohio on June 12, 1994, and had a second ceremony at San Ysidro Ranch in California. He lived in Indian Hill, Ohio.

Armstrong underwent bypass surgery on August 7, 2012 to relieve blocked coronary arteries. Although he was reportedly recovering well, he developed complications in the hospital and died on August 25, in Cincinnati, Ohio, aged 82.

On September 14, Armstrong's cremated remains were scattered in the Atlantic Ocean from the USS Philippine Sea. Flags were flown at half-staff on the day of Armstrong's funeral.