He first attempted to find a post in the Office of Arms when in 1892 he applied unsuccessfully for the post of Athlone Pursuivant on the death of the incumbent, Bernard Louis Burke. In a letter dated 2 October 1892 Vicars's half-brother Peirce Mahony wrote that Sir Bernard Burke, Ulster King of Arms, was dying and urged him: "You should move at once." Burke died in December 1892, and Vicars was appointed to the office by Letters Patent dated 2 February 1893. In 1896 Arthur Vicars was knighted, in 1900 he was appointed Commander of the Royal Victorian Order (CVO) and in 1903 he was elevated to Knight Commander of the order (KCVO). He was also a fellow of the Society of Antiquaries and a trustee of the National Library of Ireland.