16 Nov 1799 Assistant Surgeon Hompesch's Mounted Riflemen.
5 Oct 1804 Assistant Surgeon 63rd (West Suffolk) Regiment of Foot.
2 Jan 1806 Staff Surgeon.
6 Apr 1806–30 May 1815 Served in the Mediterranean.
Author: Observations on Ophthalmia and its Consequences (London 1810)
1808–14 Served in the Peninsular War.
1 Aug 1811 Physician to the Forces. Appointed to the vacancy following the death in Malta of Physician to the Forces William Irvine.
9 Oct 1817 Deputy Inspector of Hospitals.
27 May 1825 Brevet Inspector of Hospitals.
21 Sep 1830 Promoted Inspector General of Hospitals.
3 Aug 1833 Retired to a family property in Dalyston at Loughrea, County Galway. It is said that he made his fortune while serving in Ceylon between 1815 and 1826, probably through dealing in opium. Shortly after settling in Galway, Farrell paid The Encumbered Estates Commissioners £14,800 for an additional 1,040 acres for his estate.1
1 July 1838 One of twenty two Inspectors General on half pay. Total Service: 38 years 6 months, Total Full Pay Service: 29 years 6 months.