Major General William Brattle (April 18, 1706 – October 25, 1776) was an American politician, lawyer, slaveowner, and militia officer who served as the Massachusetts Attorney General from 1736 to 1738. Born into a prominent Massachusetts family, Brattle inherited the estates of his father and uncle at a young age and attended Harvard College, fully graduating from the college in 1725. He proceeded to dabble in preaching, law, and medicine before switching to a career in politics and military service in 1729; Brattle was elected to the colony's House of Assembly and commissioned into the colonial militia both in that year.

Over the course of the 1730s, Brattle continued to be involved in politics. In addition to establishing his own private law practice, he was also appointed as the colony's Attorney General in 1736, though Brattle never prosecuted anyone as attorney general due to resistance from Governor Jonathan Belcher. In 1745, he was appointed as the commander of the garrison at Castle William after King George's War broke out, though Brattle saw no military action. He married twice, the first time in 1727 and the second in 1755. Though Brattle's marriages produced nine children, only two of them survived to adulthood.

During the early years of the American Revolution, Brattle was a leader of colonial opposition to the British Crown, though by the 1770s he had gradually shifted to the Loyalist camp. In 1774, Brattle unwittingly sparked the Powder Alarm, leading to a riot in which armed mobs forced him to flee to Boston. In 1775, the American Revolutionary War broke out, and the Continental Army began besieging Boston. When the British evacuated the city in 1776, Brattle went with them to Nova Scotia, where he died several months later. In the 21st century, Brattle's ownership of slaves has come under increasing scrutiny.

William Brattle was born on April 18, 1706 in Cambridge, Massachusetts. He was born into a prominent Massachusetts family which had emigrated from England during the early 17th century as part of the waves of Puritan migration. His father, also named William, was a Congregationalist clergyman and fellow of the Royal Society who had served as minister of the First Parish in Cambridge from 1696 to 1717. Brattle's mother was Elizabeth Brattle (née Hayman), who married his father on November 3, 1697 in Boston. Brattle had only one sibling, an older brother named Thomas who died at a young age.

His father died in Cambridge on February 15, 1717, and Brattle inherited his estate along with that of Brattle's uncle Thomas. In 1718, he began attending Harvard College. Brattle graduated four years later with a Bachelor of Arts degree, before graduating again with a master's degree in 1725. Soon after graduating, he began a career in preaching, aiming to become the town clergyman of Ipswich. Discouraged by the poor reception he faced there, Brattle switched careers and began working as a physician in 1726, with many of his patients being members of prominent local families or Harvard students.

In December 1726, he accompanied a diplomatic expedition under Lieutenant Governor of Massachusetts William Tailer to the Wabanaki Confederacy as a physician. On November 23, 1727, Brattle married Katherine Saltonstall, the daughter of the governor of Connecticut, Gurdon Saltonstall. In the same year, he arranged for the construction of a large Georgian-style mansion in Cambridge, which eventually became known as the William Brattle House or "Old Brattle House" and was described by the British-born writer James H. Stark as "the resort of the fashion and style of this section of the country."

In 1729, Brattle "plunged immediately into public affairs." He was elected to serve on the Cambridge board of selectmen and also as a representative in the Massachusetts House of Assembly, in addition to being appointed as a justice of the peace (JP). In the same year, Brattle was commissioned into the Massachusetts Militia at the rank of major along with joining the Ancient and Honorable Artillery Company of Massachusetts. Despite his youth, he quickly joined in the ongoing political struggle in the House of Assembly between populist assemblymen and Governor William Burnet on the side of the former.

Brattle served on the committees which welcomed the new governor Jonathan Belcher in 1730 and delineated Massachusetts' border with Rhode Island in 1733, though he declined to sit on the committee that delineated the border with Connecticut as a result of feeling that he already had enough experience. While serving in the 1st Regiment of Militia of Middlesex, Brattle wrote the military training manual Sundry Rules and Directions for Drawing up a Regiment, which was published in 1733; "many an English or American officer packed [the manual] in his haversack" while fighting in the French and Indian War.