He was about 28 years old, and a lance corporal in the 84th Regiment (later the 2nd Battalion, York and Lancaster Regiment), British Army during the Indian Mutiny when the following deed took place on 6 October 1857 at Lucknow, British India for which he was awarded the VC:

For conspicuous gallantry at Lucknow, on the 6th of October, 1857, in going out with Serjeants Glinn and Mullins and private Mullins, to rescue Lieutenant Gibaut, who, in carrying out water to extinguish a fire in the breastwork, had been mortally wounded, and lay outside. They brought in the body under a heavy fire. Lance-Corporal Sinnott was twice wounded. His comrades unanimously elected him for the Victoria Cross, as the most worthy. He had previously repeatedly accompanied Lieutenant Gibaut when he carried out water to extinguish the fire. Despatch from Lieutenant-General Sir James Outram, ,Bart., G.C.B., dated 2nd December 1857.^[1]

Elected by the regiment. He later achieved the rank of Sergeant. He died at Clapham, London on 20 July 1896.

His Victoria Cross is displayed at The York & Lancaster Regiment Museum, Rotherham, South Yorkshire, England.

Listed in order of publication year

• The Register of the Victoria Cross (1981, 1988 and 1997)
• Clarke, Brian D. H. (1986). "A register of awards to Irish-born officers and men". The Irish Sword. XVI (64): 185–287.
• Ireland's VCs ISBN 1-899243-00-3 (Dept of Economic Development, 1995)
• Monuments to Courage (David Harvey, 1999)
• Irish Winners of the Victoria Cross (Richard Doherty & David Truesdale, 2000)

• Location of grave and VC medal (Surrey)