Worried about his brother Joseph, who had joined the fighting and died, Warren went to search for him after the battle was over.

A British sentry told John he could not pass and then bayoneted him as a warning, forcing the depressed Warren to go back to Cambridge.

After his brother's death, Warren volunteered for service and was made a senior surgeon at the hospital in Cambridge.

Warren returned to Boston in 1777 to continue his medical practice while still serving as a military surgeon in the army hospital there.

[4] While Warren had suffered from heart disease for many years,[5] he died on April 4, 1815, from inflammation of the lungs at age 61.

When church and family crypts were cleared by order of the town for public health reasons, later in the 1800s, his buried remains were removed to Forest Hills Cemetery.

Warren was of middle height, and carried himself with a military bearing of a gentleman, but with an agreeable nature.