19 Feb 1836 Commissioned Assistant Surgeon 77th (East Middlesex) Regiment of Foot vice Assistant Surgeon John Poyntz Munro who resigned his commission.
Malta 5 Dec 1837 Assistant Surgeon 77th Foot. On duty with the service companies from 13 Oct 1837.
Malta 24 Nov 1838 On leave until 28 Aug 1839.
Malta 6 Jan 1839 To England on leave.
Malta 14 Mar 1839 Returned from leave.
Malta 1 Oct 1839 To England on leave.
Malta 31 Jan 1840 Returned from leave.
Malta 17 Mar–17 June 1841 On leave. Assistant Surgeon 77th Foot.
Malta 8 Feb 1842 Left for the Ionian Islands.
22 May 1846 Promoted Staff Surgeon of the 2nd Class vice Staff Surgeon of the 2nd Class Alexander George Home, who became Surgeon 2nd Dragoon Guards on the retirement of Surgeon William Steel.
3 Oct 1848 Surgeon 77th (East Middlesex) Regiment of Foot.
28 Mar 1854 Staff Surgeon 1st Class.
Malta 27 Mar–8 Apr 1854 To Turkey via Malta. Was in the battles of Alma, Inkerman, and Balaklava, and at the siege of Sebastopol.
8 April 1854–1856 Served in the Crimean War as personal physician to Field Marshal Lord Raglan. When the latter died of dysentery on 28 June 1855, Prendergast accompanied Raglan's remains to England on HMS Caradoc, which proceeded to Malta from the Crimea. It reached Bristol on 24 July 1855.
1857 In charge of the Medical Division at Fort Pitt hospital.
2 Mar 1858 Awarded by the Sultan the Imperial Order of the Medjidie (5th Class) for his distinguished services before the enemy during the war against Russia.
28 Jan 1862 Deputy Inspector General of Hospitals.
1 May 1863 Retired to half-pay.