Lieutenant-Colonel John Blackadder (14 September 1664 – 31 August 1729) was a Scottish soldier who served with the Cameronian Regiment during the late seventeenth and early eighteenth centuries.
The fifth son of dissenting minister John Blackadder, he was a devout Calvinist, and joined the Cameronians – a predominantly religious regiment – as a volunteer cadet when they were raised in 1689 to fight for King William III.
He soldiered with the regiment through the campaign in Flanders, where he was court-martialled and later pardoned for killing an officer in a duel, and then during the War of the Spanish Succession.
He was wounded at the Battle of Blenheim, and twice wounded at the siege of Lille; after the Battle of Malplaquet he was promoted to lieutenant-colonel, and took command of the regiment.
He resigned his commission two years later, and retired to Edinburgh.
In later life he focused his work on ecclesiastical matters, becoming a member of the General Assembly of the Church of Scotland.
During the Jacobite rising of 1715 he was appointed colonel of a regiment raised in Glasgow to guard the city, and after the war made deputy-governor of Stirling Castle.