- "Stand your ground, men! Don't fire unless fired upon! But if they mean to have a war, let it begin here!"
- ―John Parker to his troops before the Battle of Lexington, 1775.[src]
Parker was born in Lexington to Josiah Parker and Anne Stone. He fought during the French and Indian War, fighting in both the Siege of Louisbourg in 1758 and the Battle of the Plains of Abraham in 1759. It was this military experience that likely led to his election as captain of the militia.
On 19 April 1775, Parker was in poor health as he was suffering from tuberculosis. However, he led the militia when the British Army attacked Lexington. When they opened fire, most of his men broke ranks, so he told the Assassin Connor to travel to nearby Concord and warn James Barrett, another militia captain.
Later that day, Parker joined the Continental Army and rallied his men to attack the regulars returning to Boston in an ambush known as "Parker's Revenge". Parker and his men participated in the subsequent Siege of Boston. However, he was unable to serve in the Battle of Bunker Hill in June, and died of tuberculosis the following September.