Mitscher was born in Hillsboro, Wisconsin on January 26, 1887, the son of Oscar and Myrta (Shear) Mitscher. Mitscher’s grandfather, Andreas Mitscher (1821–1905), was a German immigrant from Traben-Trarbach. His other grandfather, Thomas J. Shear, was a member of the Wisconsin State Assembly. During the western land boom of 1889, when Marc was two years old, his family resettled in Oklahoma City, Oklahoma, where his father, a federal Indian agent, later became that city’s second mayor. His uncle, Byron D. Shear, would also become mayor.

An indifferent student with a lackluster sense of military deportment, Mitscher’s career at the naval academy did not portend the accomplishments he would achieve later in life. Nicknamed after Annapolis’s first midshipman from Oklahoma, Peter Cassius Marcellus Cade, who had “bilged-out” in 1903, upperclassmen compelled young Mitscher to recite the entire name as a hazing. Soon he was referred to as “Oklahoma Pete”, with the nickname shortened to just “Pete” by the winter of his youngster (sophomore) year.

Mitscher attended elementary and secondary schools in Washington, D.C. He received an appointment to the United States Naval Academy at Annapolis, Maryland in 1904 through Bird Segle McGuire, then U.S. Representative from Oklahoma.

This time the stoic Mitscher worked straight through, and on June 3, 1910, he graduated 113th out of a class of 131. Following graduation he served two years at sea aboard USS Colorado, and was commissioned ensign on March 7, 1912. In August 1913, he served aboard USS California on the West Coast. During that time Mexico was experiencing a political disturbance, and California was sent to protect U.S. interests and citizens.

Mitscher was assigned to the armored cruiser USS North Carolina, which was being used to experiment as a launching platform for aircraft. The ship had been fitted with a catapult over her fantail. Mitscher trained as a pilot, earning his wings and the designation Naval Aviator. Mitscher was one of the first naval aviators, receiving No. 33 on June 2, 1916. Almost a year later, on April 6, 1917, he reported to the renamed armored cruiser USS West Virginia for duty in connection with aircraft catapult experiments.

At this early date the Navy was interested in using aircraft for scouting purposes and as spotters for direction of their gunnery. Lieutenant Mitscher was placed in command of NAS Dinner Key in Coconut Grove, Florida. Dinner Key was the second largest naval air facility in the U.S. and was used to train seaplane pilots for the Naval Reserve Flying Corps. On July 18, 1918, he was promoted to lieutenant commander. In February 1919, he transferred from NAS Dinner Key to the Aviation Section in the Office of the Chief of Naval Operations, before reporting to Seaplane Division 1.

On May 10, 1919, Mitscher was among a group of naval aviators attempting the first transatlantic crossing by air. Among the men involved was future admirals Jack Towers and Patrick N. L. Bellinger. Mitscher piloted NC-1 under the command of Bellinger, one of three Curtiss NC flying boats that attempted the flight. Taking off from Newfoundland, he nearly reached the Azores before heavy fog caused loss of the horizon, making flying in the early aircraft extremely dangerous. What appeared to be fairly calm seas at altitude turned out to be a heavy chop, and a control cable snapped while setting the aircraft down. Mitscher and his five crewmen were left to sit atop the upper wing of their “Nancy” while they waited to be rescued. Of the three aircraft making the attempt, only NC-4 successfully completed the crossing. For his part in the effort Mitscher received the Navy Cross, the citation reading:

Mitscher was also made an officer of the Order of the Tower and Sword by the Portuguese government on June 3, 1919.

On October 14, 1919, Mitscher reported for duty aboard Aroostook, a minelayer refitted as an “aircraft tender” that had been used as a support ship for the “Nancys” transatlantic flight. He served under Captain Henry C. Mustin, another pioneering naval aviator. Aroostook was assigned temporary duties as flagship for the Air Detachment, Pacific Fleet. Mitscher was promoted to commander on July 1, 1921. In May 1922, he was detached from Air Squadrons, Pacific Fleet (San Diego, California) to command Naval Air Station Anacostia, D.C.

After six months in command at Anacostia he was assigned to a newly formed department, the Navy Bureau of Aeronautics. Here as a young aviator he assisted Rear Admiral William Moffett in defending the Navy’s interest in air assets. General Billy Mitchell was advancing the idea that the nation was best defended by an independent service which would control all military aircraft. Though Mitscher was not a vocal member of the Navy’s representatives, his knowledge of aircraft capabilities and limitations was instrumental in the Navy being able to answer Mitchell’s challenge and retain their own airgroups. The debate culminated in the hearings before the Morrow Board, convened to study the best means of applying aviation to national defense. Mitscher testified before the board on October 6, 1925. General Mitchell sought public support for his position by taking his case directly to the people through the national press. For this action Mitchell was summoned for a court-martial. One of the witnesses called by the prosecution was Mitscher. In the end the Navy was left with its own air resources, and was allowed to continue to develop its own independent aviation branch.

During this period Mitscher was assigned command of the air group for the newly commissioned aircraft carrier Saratoga. Mitscher was the first person to land an airplane onto the flight deck of Saratoga as he brought his air group aboard. The vessel conducted mock attacks against the Panama Canal and Pearl Harbor in a series of Fleet Problem exercises. The key lesson learned by the naval aviation officers during these exercises was the importance to locate and destroy the other side’s flight decks as early as possible, while still preserving your own. In 1938, Mitscher was promoted to captain.

Between June 1939 and July 1941, Mitscher served as assistant chief of the Bureau of Aeronautics.

Mitscher’s next assignment was as captain of the Yorktown-class aircraft carrier USS Hornet, being fitted out at Newport News Shipbuilding in Newport News, Virginia. Upon her commissioning in October 1941 he assumed command, taking Hornet to the Naval Station Norfolk for her training out period. She was there in Virginia when the Japanese attacked Pearl Harbor. Newest of the Navy’s fleet carriers, Mitscher worked hard to get ship and crew ready for combat. Following her shake-down cruise in the Caribbean, Mitscher was consulted on the possibility of launching long-range bombers off the deck of a carrier. After affirming it could be done, the sixteen B-25 bombers of the Doolittle Raid were loaded on deck aboard Hornet for a transpacific voyage while Hornet’s own flight group was stored below deck in her hangar. Hornet rendezvoused with Enterprise and Task Force 16 in the mid-Pacific just north of Hawaii. Under the command of Admiral Halsey, the task force proceeded in radio silence to a launch point 650 miles (1,050 km) from Japan. Enterprise provided the air cover for both aircraft carriers while Hornet’s flight deck was taken up ferrying the B-25s. Hornet, then, was the real life “Shangri-la” that President Roosevelt referred to as the source of the B-25s in his announcement of the bombing attack on Tokyo.

Prior to the Midway operation Mitscher had been promoted to Admiral in preparation for his next assignment, the command of Patrol Wing 2. Though Mitscher preferred to be at sea, he held this command until December when he was sent to the South Pacific as Commander Fleet Air, Nouméa. Four months later in April 1943, Halsey moved Mitscher up to Guadalcanal, assigning him to the thick of the fight as Commander Air, Solomon Islands (COMAIRSOLS). Here Mitscher directed an assortment of Army, Navy, Marine and New Zealand aircraft in the air war over Guadalcanal and up the Solomon chain. Said Halsey: “I knew we’d probably catch hell from the Japs in the air. That’s why I sent Pete Mitscher up there. Pete was a fighting fool and I knew it.” Short on aircraft, fuel and ammunition, the atmosphere on Guadalcanal was one of dogged defense. Mitscher brought a fresh outlook, and instilled an offensive mindset to his assorted air commands. Mitscher later said this assignment managing the constant air combat over Guadalcanal was his toughest duty of the war.

On 11 May 1945 Mitscher’s flagship Bunker Hill was struck by kamikazes, knocking her out of the operation and causing much loss of life. Half of Mitscher’s staff officers were killed or wounded, and Mitscher was forced to shift his command to Enterprise. Enterprise at that time was functioning as a “night carrier”, launching and recovering her aircraft in the dark to protect the fleet against bomber and torpedo aircraft slipping in to attack the fleet in the relative safety of night. When Enterprise was struck by kamikaze attack as well, Mitscher had to transfer once more, this time to USS Randolph, the Essex-class aircraft carrier that had been damaged by a long-range kamikaze attack at Ulithi. Throughout this period Mitscher repeatedly led the fast carriers northward to attack airbases on the Japanese home islands. Commenting on Admiral Mitscher upon his return from the Okinawa campaign, said Admiral Nimitz “He is the most experienced and most able officer in the handling of fast carrier task forces who has yet been developed. It is doubtful if any officer has made more important contributions than he toward extinction of the enemy fleet.”

By July 1946, when he returned to the United States to serve as Deputy Chief of Naval Operations (Air), Mitscher received, among other awards, two Gold Stars in lieu of a second and third Navy Cross and the Distinguished Service Medal with two Gold Stars.

He served briefly as commander 8th Fleet and on March 1, 1946, became Commander-in-Chief, U.S. Atlantic Fleet, with the rank of admiral.

While serving in that capacity, Mitscher died on 3 February 1947 of a coronary thrombosis at Norfolk, Virginia at the age of 60. He was buried in Arlington National Cemetery.

In 1989, Mitscher was inducted into the International Air & Space Hall of Fame at the San Diego Air & Space Museum.