10 Nov 1825 Hospital Assistant.
9 Feb 1826 Assistant Surgeon 20th (East Devonshire) Regiment of Foot.
3 Sept 1829 Assistant Surgeon 23rd (Royal Welsh Fusiliers) Regiment of Foot vice Assistant Surgeon John Morrison who retired.
11 Oct 1831 Appointed Assistant Surgeon 8th West India Regiment through exchange with Assistant Surgeon Edward McIver half-pay 8th West India Regiment.
9 July 1832 Recalled from half-pay 8th West India Regt and appointed Staff Assistant Surgeon vice Michael Fogerty promoted surgeon 22nd Foot.
2 July 1841 Promoted Surgeon 75th Regiment of Foot, vice Surgeon Edward Smith Graham, appointed Surgeon 4th Light Dragoons.
13 May 1842 Staff Surgeon 2nd Class by exchange with Staff Surgeon 2nd Class James Sidey.
30 Apr 1847 Promoted Surgeon 91st (Argyllshire) Regiment of Foot vice Surgeon Samuel Maitland Hadaway who exchanged from 91st Foot to be Staff Surgeon of the Second Class vice Forrest.
21 May 1850 Staff Surgeon 1st Class.
28 Mar 1854 Deputy Inspector General.
5 Feb 1856 Made a Companion of the Most Honourable Order of the Bath for his services in Turkey.
2 Mar 1858 Awarded the Imperial Order of Medjidie (4th Class) for his services in the Crimea.
31 Dec 1858 Inspector General.
Malta 14 Feb 1859 Arrived from Gibraltar. The opening of the Mdina Sanatorium, the formation of a proper encampment for musketry instruction at St George's Bay, and the conversion of the Palace of St Julian as a hospital for St George's Camp were three key improvements implemented under IG John Forrest for the health of the troops.
16 Aug 1859 Honorary Physician to the Queen.
Malta 1860 Inspector General.
Malta 1 July 1861 Left for England.
9 Nov 1861 Retired on half-pay. The subsequent vacancy was filled by Deputy Inspector General of Hospitals Thomas David Hume, who was promoted Inspector General.