[1] It seems that Tonnochy did not complete his studies at Cambridge, choosing instead to try for a new cadetship in the Hong Kong Civil Service, by competitive examination in 1862.
In this he was successful, along with fellow candidates Cecil Clementi Smith and Walter Meredith Deane, the three of them comprising the first appointments on merit in a service that was beginning to modernise.
[2] Tonnochy worked his way up to hold many posts including Coroner, Assistant Harbour Master, Police Magistrate, acting Colonial Treasurer (when James Russell was absent), acting Colonial Secretary and as judge in the Royal Navy's Vice Admiralty Court of Hong Kong from 1879 to 1882.
[3] Tonnochy was unmarried and died aged 41 after serving as acting Administrator of Hong Kong in early 1882.
Unlike most colonial officials in Hong Kong at the time, Tonnochy was never honoured with any titles.