He entered the army as a cornet in the 12th Light Dragoons in 1813, was promoted lieutenant in 1815, and was with the regiment at the Battle of Waterloo.
Two years afterwards he was made a CB During the First Sikh War his regiment formed part of the force which held Ferozepore under Sir John Hunter Littler.
At the Battle of Ferozeshah in 1845 Reed commanded a brigade (including his own regiment) of Littler's division and was ordered to attack the strongest part of the Sikh entrenchments where there was a large number of heavy guns served with grape and canister.
When the Indian Mutiny broke out in 1857 he became provisional commander-in-chief on the death of General Anson from cholera, as the senior officer in the Bengal presidency, until Sir Patrick Grant arrived.
On the death of Sir Henry Barnard, Reed assumed command of the field force but the exertions and anxieties of that position were too much for him.