[2] Halkett began his military career in the Dutch Guards and served in various companies for three years, leaving as a captain in 1795.

[2] On 28 July 1803, a letter of service was issued to Major Halkett (and to Lieutenant Colonel von der Decken) empowering him "to raise a battalion of infantry with an establishment of four hundred and fifty-nine men" and offering him the rank of lieutenant colonel should he increase the number to eight hundred men.

On 17 November 1803, Halkett was promoted to Lieutenant Colonel and given command of the 2nd Light Infantry Battalion.

[2] At the Battle of Salamanca (22 July 1812), he commanded 1st Brigade of the 7th Division under Major General Hope.

He was promoted to lieutenant general on 22 July 1830 and appointed Commander-in-Chief of the Bombay Army in January 1832.