Hay purchased a lieutenantcy in the Grenadier Guards in 1841. He purchased a captaincy in 1846 and was promoted lieutenant-colonel without purchase in 1854 and Colonel in 1860. In 1866 he transferred to the 17th Lancers. He was president of the Zoological Society of London from 16 January 1868. His ornithological works were published privately in 1881 by his nephew, Captain Robert George Wardlaw-Ramsay, with a memoir by Dr W. H. Russell, and the attribution Walden is used in taxonomic listings.