During the 1760s, despite having previously been a supporter of Crown governors, Brattle emerged as a leader of
colonial opposition to British policies toward the Thirteen Colonies. Disappointed by the fact that
Thomas Hutchinson was appointed as chief justice of the Superior Court of Judicature in 1761, he led the anti-government faction in the Governor's Council, while in the House of Assembly the faction was led by fellow populist
James Otis Jr. On November 5, 1765, in lieu of the traditional
Guy Fawkes Night, in which mobs from Boston's
North and
South Ends battled over the possession of effigies of the
pope and
Stuart pretender, Brattle and fellow populist
Ebenezer Mackintosh headed a procession to symbolise the militia and mobs joining forces, angering Governor
Francis Bernard. In 1767 and again from 1772 to 1773, Brattle served with Hutchinson and
John Hancock in a committee which conducted boundary negotiations with authorities in
New York. Brattle and
James Bowdoin were elected to the Governor's Council in 1769, though this was blocked by Bernard, who alleged that the two men were "the Managers of all late Opposition in the Council to the Kings Government." Bernard also revoked Brattle's colonelcy of the 1st Regiment of Militia of Middlesex, while Brattle sent a private letter to
Lord Dartmouth explaining the situation and reaffirming his loyalty to
the Crown. In the spring of 1770, Brattle was elected by voters in Cambridge to the House of Assembly, where he served on a committee that managed the construction of
gunpowder magazines in the colony. Despite having previously supported the anti-government
Sons of Liberty, Brattle publicly split with them in January 1773 over his argument in a Cambridge town meeting on December 1772 that judges in Massachusetts should have fixed salaries to make them independent of both the governor and House of Assembly. Brattle's argument led to a
war of letters between him and a local attorney,
John Adams, which brought the latter into the political limelight. Shipton argued that Brattle had not intended to provoke a controversy while Adams had "tried to split legal hairs". From that point onwards, "Brattle could be counted among the increasing numbers of the old political élite who, while initially having opposed British policy, feared that the growth of popular politics threatened the social order." To reward him for his role in the affair, Hutchinson promoted Brattle to the rank of
major general in 1773. On August 27, 1774, Brattle sent a letter to Governor
Thomas Gage, informing him that only British-owned gunpowder remained in the
Old Powder House near Boston. Four days later, Gage dispatched roughly 260 soldiers from the
4th Regiment of Foot to remove the gunpowder. At the same time, Gage lost the letter Brattle wrote to him, which was soon found by local
Patriots and publicized.
Rumors emerged that violence had broken out during the powder's removal; an angry mob proceeded to Brattle's mansion, forcing him to flee to Castle William seeking British protection. However, the mobs soon dispersed as it became clear that no violence had actually occurred. On September 5, 1774, several newspapers in Boston published a letter from Brattle in which he insisted that he had not persuaded Gage to remove the powder; according to Brattle's account, Gage had requested a full account of the Old Powder House's contents from him, and he had merely complied. Brattle continued to live in Boston when the
American Revolutionary War broke out in April 1775, with the
Continental Army besieging the city. On March 17, 1776,
General Sir William Howe, having decided his position was untenable, ordered the British garrison in Boston to be evacuated to
Halifax, Nova Scotia. Brattle went with them, and died in Halifax on October 25, 1776. After a ceremony at
St. Paul's Church, he was interred at the
Old Burying Ground on October 26. ==Personal life, family and legacy==