[1] Trained as a doctor, Brooks was an officer of the Reading, Massachusetts militia when the American Revolutionary War broke out, and led his troops in the Battles of Lexington and Concord.

In 1777 he was part of the relief force for the Siege of Fort Stanwix, and led a successful assault against British positions in the key Second Battle of Saratoga.

After the war he returned to medical practice, but continued to be active in the state militia, helping to put down Shays' Rebellion in 1787.

In his free time he engaged in military drills with other local boys and carefully watched the maneuvers of British Army troops stationed in nearby Boston.

[4] When Paul Revere gave the alarm that sparked the Battles of Lexington and Concord on April 19, 1775, Brooks, then 22 and a major in the Reading militia, marched with his unit in response.

His troops were among the first to reach Concord as the British took the road back to Boston, and are credited with beginning the running battle that took place.

He then joined the Continental Army in May 1775 as a major in Bridge's Regiment, and was among the troops sent to fortify Breed's Hill on the night of June 16–17.

[7] After the British withdrawal from Boston, Brooks' regiment next saw action in the October 1776 Battle of White Plains, and was in General George Washington's retreat across New Jersey afterward.

[6] The 8th Massachusetts was among the forces Benedict Arnold led in relief of the Siege of Fort Stanwix in upstate New York, and was present at the Battles of Saratoga.

[9] In a letter to a friend Brooks describes the harsh conditions of the camp at Valley Forge,[10] as he mentions the “poor brave fellows” that were living in tents “bare-footed, bare-legged, bare-breeched”.

Brooks was temporarily named adjutant to General Charles Lee when the army followed the British across New Jersey in 1778, engaging them in the Battle of Monmouth.

He then carried letters back to the army headquarters, and took part in actions orchestrated by Washington supporters to put down any ideas of mutiny.

)[14] Historian Richard Kohn writes that details are lacking of Brooks' actions and motivations in the critical days of the conspiracy in February and March 1783, but describes his role in the affair as "crucial".

[20] Brooks was offered a position as brigadier general in the United States Army by George Washington when war was threatened with France in 1797, but refused.

"[29] The Panic of 1819 and the granting of statehood to Maine (which was until 1820 part of Massachusetts) introduced fractures in the strong Federalist party system in the state.

[31] Nine amendments produced by the convention were eventually approved, but Federalist leaders managed to block most of the substantive reforms that had been sought.