Lieutenant Colonel Henry Joseph O'Brien was educated at Trinity College Dublin, where he graduated AB and MB in 1864 and BCh in 1865.
He entered the Army Medical Department as an assistant surgeon on 2 October 1865 and retired with the rank of Brigade-Surgeon-Lieutenant-Colonel on 30 June 1896. He served in the Afghan war in 1878–1880, receiving the medal. In 1881, he published in the Lancet a case report of
passage of a pin through the alimentary canal.
Service Record — Henry Joseph O'Brien
2 Oct 1865 Staff Assistant Surgeon.
Malta 21 Sept 1866 Arrived from England.
Malta 1867 On garrison duty.
Malta 15 Feb 1868 Appointed Assistant Surgeon 1st/8th (The King's) Regiment of Foot vice Assistant Surgeon John Stuart, appointed to the staff.
Malta 9 Apr 1868 To England.
Malta 30 June 1868 Returned to Malta.
Malta 9 Oct 1868 Left for the East Indies.
25 Jan 1871 Appointed Staff Assistant Surgeon from 8th Foot vice Staff Assistant Surgeon Albert Halahan L'Estrange appointed to 8th Foot.
1871 On duty at Chapel-en-le-Frith Derbyshire.
1872–1873 On duty in Devonport.
1 Mar 1873 Promoted Surgeon.
1874 Moved to Bengal.
1875–1879 On duty in Bengal.
2 Oct 1877 Promoted Surgeon-Major.
1878–1880 Served in the Second Afghan War.
Jan 1880–1882 Served in Devonport.
Sept 1882 Moved from Devonport to Cork.
2 Oct 1885 Promoted Surgeon-Lieutenant-Colonel.
14 Feb 1892 Brigade-Surgeon-Lieutenant-Colonel.
30 June 1896 Retired. Was employed when on the retired list at Maidstone.
1897–1899 Employed in medical charge of troops at Maidstone while on the retired list.
Aug 1899 Relinquished the medical charge of troops at Maidstone and was succeeded by Lt Col Kenneth Serjeant Wallis retired pay.