At the age of 15 he entered the East India Company's Military Seminary at Addiscombe, graduating in June 1841 and receiving a commission in the Bengal Horse Artillery.

[3] At the age of thirty-one, when a major in the Bengal Horse Artillery, Bengal Army during the Indian Mutiny, the following deed took place at the Siege of Delhi for which he and James Hills were awarded the VC: Lieutenant-Colonel Henry Tombs, C.B., and Lieutenant James Hills Date of Act of Bravery, 9th July, 1857 For very gallant conduct on the part of Lieutenant Hills before Delhi, in defending the position assigned to him in case of alarm, and for noble behaviour on the part of Lieutenant-Colonel Tombs in twice coming to his subaltern's rescue, and on each occasion killing his man.

(See despatch of Lieutenant-Colonel Mackenzie, Commanding 1st Brigade Horse Artillery, dated Camp, near Delhi, 10th July, 1857, published in the Supplement to the London Gazette of the 16th January, 1858.

)[4]For services at the siege of Delhi, Tombs was promoted brevet lieutenant-colonel and made a Companion of the Order of the Bath in January 1858.

Field Marshall Frederick Roberts, 1st Earl Roberts, another junior officer in the Bengal Horse Artillery during the Indian Rebellion, and a recipient of the VC himself (Khudaganj, 2 January 1858) later wrote:The hero of the day [when he won the VC] was Harry Tombs … an unusually handsome man and a thorough soldier.

As a cool, bold leader of men Tombs was unsurpassed: no fire, however hot, and no crisis, however unexpected, could take him by surprise; he grasped the situation in a moment, and issued his orders without hesitation, inspiring all ranks with confidence in his power and capacity.

[7]At news of Tombs's death, the Commander-in-Chief, India, Lord Napier issued a general order expressing regret at the loss of "so distinguished an officer".