He is best remembered for his tenure as Secretary of State for War between 1868 and 1874 and, with William Ewart Gladstone's support, the introduction of the Cardwell Reforms.

[1] Cardwell was employed in the Colonial Office in the late 1830s, and directly involved in drafting written instructions (sent to Sydney) to Captain William Hobson RN, as to how to 'treat with the natives' (Maori) of New Zealand;[citation needed] He became a follower and confidant of Sir Robert Peel, the Prime Minister, and held his first office under him as Financial Secretary to the Treasury between 1845 and 1846.

When the Peelites came to power in 1852, Cardwell was sworn of the Privy Council[2] and made President of the Board of Trade by Lord Aberdeen, a position he held until 1855.

[citation needed] Cardwell quickly return to office by joining Lord Palmerston's cabinet as Chief Secretary for Ireland.

Liberal prime minister William Ewart Gladstone paid little attention to military affairs but he was keen on efficiency.

[11] Cardwell as Secretary of State for War (1868–1874) designed the reforms that Gladstone supported in the name of efficiency and democracy.

The most radical change, and one that required Gladstone's political muscle, was to abolish the system of officers obtaining commissions and promotions by purchase, rather than by merit.

They warned the latter might menace the oligarchy and threaten a military coup; they preferred an inefficient army to an authoritarian state.

The rise of Bismarck's new Germany made this anti authoritarian policy too dangerous for a great empire to risk.

Gladstone then moved to drop the system without any reimbursements, forcing the Lords to backtrack and approve the original bill.

Liberals rallied to Gladstone's anti-elitism, pointing to the case of Lord Cardigan (1797–1868), who spent £40,000 for his commission and proved utterly incompetent in the Crimean war, where he led the disastrous "Charge of the Light Brigade" at the Battle of Balaklava in 1854.