The first P-26As entered service with the USAAC in early 1934. The first USAAC units to take delivery of P-26s belonged to the 20th Pursuit Group (55th, 77th, and 79th Squadrons) based at Barksdale Field, Louisiana, the 1st Pursuit Group (17th, 27th, and 94th Squadrons) based at Selfridge Field, Michigan, and the 17th Pursuit Group (34th, 73rd, and 95th Squadrons) based at March Field, California.
In 1938, P-26s were assigned to the 18th Pursuit Group (6th, 19th, 44th, 73rd, and 78th Squadrons) bassed at Wheeler Field on Oahu in Hawaii. In 1940, more P-26s reached Wheeler Field to join the 15th Pursuit Group (45th, 46th, and 47th Squadrons). The P-26s replaced P-12s and served alongside the Curtiss P-36.
The P-26s were in service with the 17th Pursuit Group for only a year, after which these planes were transferred to the 16th Pursuit Group (24th, 29th, and 78th Squadrons). The 16th Pursuit Group (24th and 29th Squadrons) set up operations at Albrook Field in the Canal Zone beginning in February of 1939. These planes were later transferred to the 37th Pursuit Group (28th, 30th, and 31st Squadrons) which flew them until May of 1941 when they were replaced by P-40Bs. Some were later transferred to the 32nd Pursuit Group (51st and 53rd Squadrons). However, by the time of Pearl Harbor, only nine P-26s remained airworthy in Central America.
P-26s were also flown by the 6th and 19th squadrons of the 18th Fighter Group based in Hawaii from 1938 onward. They were also flown by the 3rd Squadron in the Philippines.
The P-26 was a popular pilots' airplane and performed well until outclassed by more modern fighters. P-26s served in front-line units with the USAAC until 1938-40, when they began to be replaced by Seversky P-35 and Curtiss P-36A fighters. All P-26 models had been withdrawn from regular squadron use by the time of Pearl Harbor, and most surviving stateside P-26 aircraft had been relegated to mechanic training schools.
There were still some P-26s sitting on the flight line at Wheeler Field at the time of the Japanese attack on Pearl Harbor. Six of them were destroyed and one was damaged.
Most of those P-26s that had been stationed in the Philippines had been sold to the government of the Philippines by the time of the Japanese attack. The Philippine government acquired 12 P-26As beginning in July of 1941. Some of these P-26s were serving with the 6th Pursuit Squadron of the Philippine Army Air Force based at Batangas Field at the time of the Japanese attack. Despite their total obsolescence, the Filipino P-26s succeeded in scoring some victories against the Mitsubishi A6M Zero during the first few days of the Japanese attack. One of the Philippine P-26s is credited with shooting down the first Japanese plane destroyed during the early attacks on the islands. The best-known action took place on December 12, 1942, then a group of six Philippine P-26s led by Capt. Jesus Villamor shot one bomber and two Zeros with the loss of three P-26s. However, the few P-26s operated by the Philippine Army Air Force were quickly overwhelmed by the onslaught of the Japanese Zero fighters, and the surviving P-26s were destroyed on the ground by Filipinos to prevent them from falling into enemy hands.
Following Pearl Harbor, only nine P-26s remained airworthy in the Panama Canal Zone. They were replaced by P-40s in June of 1942. In November of 1942, the Fuerza Aerea de Guatemala expressed interest in acquiring these obsolescent P-26s. However, there was at that time a Congressional rule forbidding export of fighters to all Latin American nations except Brazil and Mexico. Consequently, in order to get around the restriction, the fighters were identified on transfer documents as "Boeing PT-26A" aircraft, a trainer designation which actually belonged to the Fairchild Cornell primary trainer. A total of seven P-26s were transferred to Guatemala under this ruse. Serials were 33-049, 075, 089, 123, 126, 132, and 135. The last of these, in fact the last P-26 in American service (33-89) was transferred to Guatemala on May 4, 1943.
Several of the Guatemalan P-26s were still active as trainers as late as 1957. One P-26 was obtained from Guatemala by the Planes of Fame Museum of Chino, California where it has been restored to flying condition in its original US Army markings. Another was obtained from the same source by the National Air and Space Museum of the Smithsonian Institution.