Frank A. Arnold qualified as a Licentiate of the Society of Apothecaries of London (LSA) in 1892 and as Bachelor of Medicine (MB) at the University of London in 1896. Subsequently he was awarded the Diploma in Public Health (DPH) of the Royal College of Physicians and Surgeons in 1902. He entered the public service of the Transvaal Colony in December 1902, serving initially as district medical officer of health for the Eastern Transvaal and later as assistant medical officer of health of the Transvaal (1903). In December 1905 he was granted leave and the next year was awarded the Diploma in Tropical Medicine by the University of Liverpool. Later that year he became district medical officer of health for the Northern Transvaal. Subsequently he was appointed medical officer of health of the Transvaal (1910), and medical officer of health of the Union of South Africa from July 1911. By 1914 his post was in the Department of the Interior. He was registered to practice medicine in the Transvaal Colony in 1905.
Dr Arnold published two papers in the Transvaal Agricultural Journal, one on "The maggot fly" (1906/7, Vol. 5, pp. 907) and the other "On mosquito nets" (1907/8, Vol. 6, p. 13). He became a member of the South African Association for the Advancement of Science in 1903 when he was living in Middelburg (Mpumalanga) and was still a member in 1911, having lived in Pretoria since 1906 or earlier. By 1926 he had retired and was living at or near the railway station Mara, in Limpopo.