A.J. Williams qualified as a veterinarian (MRCVS) at the Royal (Dick) Veterinary College in Edinburgh in 1898. During the Anglo-Boer War (1899-1902) he served as a regular with the Army Veterinary Department (as senior veterinary officer in the sixth Division) from November 1899 to October 1902. He published an article in the Veterinary Record of 11 January 1902 on poisonous plants in South Africa, mentioning plants such as the tulp (most species of Homeria and Moraea), pepper bush (several species of Coronopus and Lepidium), inkbush (several species of Suaeda), and Euphorbia.
After the war he returned to England where he was prmoted to captain in 1903 and served with Thorneycrofts Mounted Infantry. He saw service in Tibet (1904), Egypt (1907-1909), and in Mesopotamia (1917-1919) during World War I. From 1921 to 1923 he was assistant director-general of the Army Veterinary Service in the War Office, and from 1923 to 1924 commander of the Royal Army Veterinary School at Aldershot. In 1928, with promotion to brigadier, he became director of Veterinary Services in India until 1932, when he retired in London.