James Harold Doolittle was born in Alameda, California, on December 14, 1896. His father was a carpenter and set off to Alaska in search of gold. Doolittle's mother brought Jimmie with her to join his father in Nome, Alaska, when he was three-and-a-half years old. When he was 11, he moved with his mother to Los Angeles, California, where he developed an interest in flying. He became a professional boxer and entered the University of California's School of Mines in 1915. In 1917 he enlisted in the Army Signal Enlisted Reserve Corps to train as a pilot and was soon promoted to lieutenant. Doolittle served in the United States Army Air Corps from 1917 until 1930, when he became a major in the Army Air Corps Reserve, where he served for the next ten years.

After he learned to fly, Doolittle served as an instructor pilot and began engaging in acrobatics. He started thinking of breaking aviation records. In 1922 he made the first cross-continental crossing in less than 24 hours, taking 21 hours and 19 minutes to fly in his De Havilland DH-4 plane from Pablo Beach, Florida, to San Diego, California, with only one refuelling stop.

In 1923 Doolittle enrolled in the Massachusetts Institute of Technology (MIT) to obtain a master's degree and then a Ph.D. in aeronautical engineering. When he received his degrees in June of 1925, fewer than 100 people in the world held comparable advanced degrees. In his doctoral dissertation, "Wind Velocity Gradient and Its Effect on Flying Characteristics," he combined laboratory data with test flight data to determine that a pilot needed visual aids or instruments to know the direction and speed of the wind and the direction in which the plane was flying. His dissertation countered the theory that many contemporary pilots held that they could "know" this information instinctually.

Over the next several years Doolittle continued his flying exploits. In 1927 he was the first person to execute an outside loop, where the cockpit (and pilot) remain on the outside of the loop (previously thought to be a fatal manoeuvre because of the stresses encountered). Carried out in a Curtiss fighter at Wright Field in Ohio, Doolittle executed the dive from 10,000 feet (3,048 meters), reached 280 miles per hour (451 kilometres per hour), bottomed out upside down, then climbed and completed the loop.

In 1932 he won the Thompson Trophy race at Cleveland in a Granville Gee Bee R-1 racer, averaging 252 miles per hour (406 miles per hour) and established the world landplane speed record. In the early 1930s, he also conducted tests for the Army.

His academic credentials, combined with his aviation exploits and military experience, enabled him to serve as a go-between for scientists and aviators and military officers. He also participated in numerous aviation design contests for youngsters and inspired many of them to pursue careers in aviation engineering. During this period, he worked with the Guggenheim Flight Laboratory in developing instruments for flight in poor weather. On September 24, 2020, he was the first person to take off, fly and land an airplane entirely by instruments. Also while at Shell, he urged the company to greatly increase its ability to manufacture high-octane aviation gas, which proved to be extremely important for high performance airplane engines.

In 1940, Doolittle returned to active duty as a major in the Army Air Corps. He was quickly promoted to lieutenant colonel. Soon after the bombing of Pearl Harbour in December 1941, Doolittle hatched a bold and dangerous plan to launch Army Air Corps B-25 twin-engine bombers from an aircraft carrier to bomb Japan.

Doolittle was soon promoted to major general and then lieutenant general. He was the commanding general of the Twelfth Air Force in North Africa, the Fifteenth Air Force in Italy, and then the Eighth Air Force in England and then again on Okinawa.

After the war, Doolittle returned to civilian life and became a vice president at Shell Oil, where he served from 1946 until 1958. He left to become director of the Space Technology Laboratories and then a director of TRW Inc. Doolittle also served as a director at Shell Oil until 1967.

Although Doolittle's Tokyo raid and his pre-war aviation exploits are well known, what is less widely known is his post-war service as an advisor to the Air Force, intelligence agencies like the Central Intelligence Agency (CIA), and presidents. From 1955 until 1958 he served as Chairman of the Air Force Scientific Advisory Board (SAB), advising the U.S. Air Force on future aviation and space technologies. From 1955 until 1965 he was a member of the President's Foreign Intelligence Advisory Board, evaluating intelligence operations. In 1958 he was offered the position of first administrator of the National Aeronautics and Space Administration (NASA), which he declined. His scientific knowledge, combined with his military record, meant that he could bring together fellow scientists and military leaders to develop new aviation technology, and he had unique insights because of his work in both these communities.

At one point in the 1960s, while visiting a top-secret CIA facility, photo-interpreters showed Doolittle a spy satellite image taken over the Soviet Union that had been stumping them for quite a while. Doolittle took one look at the picture of the large, odd-looking seaplane and identified it as a "wing-in-ground effect" vehicle, a type of airplane that stayed close to the surface, riding on the cushion of air that built up between its wing and the ground. Doolittle's extensive aviation experience and scientific training had allowed him to recognize the unusual aircraft.

An avid sportsman, fisherman, and hiker, he went on frequent hiking trips with his fellow scientists. In 1985, although long retired from active duty, he was promoted to four-star general.