Production was started against an order for three from the Irish Free State and 21 Trainers from the Royal Air Force. The RAF required a replacement for the wooden Avro 504, and after three years of trials against other machines such as the Hawker Tomtit it was adopted as their basic trainer, supplanting the 504 in 1933 and remaining in this role until 1939. As well as the 21 Trainers a total of 381 Tutors and 15 Avro 646 Sea Tutors were eventually ordered by the RAF. RAF units to operate the type in quantity included the Royal Air Force College, the Central Flying School and Nos. 2, 3, 4 and 5 Flying Training Schools.
Subsequently, the Model 621 achieved substantial foreign sales. A.V. Roe and Co exported 29 for the Greek Air Force, six for the Royal Canadian Air Force, five for the Kwangsi AF, three for the Irish AF (where it was known as the Triton) and two for each of the South African and Polish AFs. In addition 57 were licence built in South Africa, and three licence built by the Danish Naval Shipyard.
A total of 30 Tutors were exported to the Greek Air Force and at least 61 were licence built in Greece by KEA. A number of Greek Tutors was incorporated in combat squadrons after Greece's entrance in WWII, used as army co-operation aircraft.
Known for its good handling, the type was often featured at air shows. Over 200 Avro Tutors and five Sea Tutors remained in RAF service at the beginning of the Second World War.
The 621 was designed as a military trainer and few reached the civil registers. In the 1930s, in addition to 10 prototypes and demonstrators, two were used by Alan Cobham's Flying Circus and two trainers were retired from the RAF into private use. One 621 was used from new by Australian National Airways. After the war another four ex-RAF 621s appeared on the civil register.