Born in Weymouth, Massachusetts, he was a nephew of Abigail Adams. His father was Richard Cranch, an English-born clockmaker and Massachusetts legislator and his mother was Mary Smith, the elder sister of Abigail Smith Adams. His uncle by marriage was John Adams, the second President of the United States. His first cousin was John Quincy Adams, the sixth President. William Cranch graduated from Harvard College with honors in 1787 and was admitted to the Massachusetts bar in 1790. From 1791 to 1800, Cranch worked as a legal agent for a real estate firm in Washington.
When land speculation bankrupted him, his uncle John Adams rescued him by appointing him to be Inspector of Public Buildings in 1800 and then in 1801 to be judge of the District of Columbia circuit court, where he served until his death. Cranch, like William Marbury, was one of the "Midnight Judges" appointed under the Judiciary Act of 1801 that led to the Supreme Court case Marbury v. Madison. The nomination was put forth on February 28, 1801, and Cranch was confirmed by the United States Senate on March 3, 1801, receiving his commission the same day.
On February 21, 1806, President Thomas Jefferson elevated Cranch to Chief Judge, that seat having been vacated by William Kilty. Cranch's elevation was confirmed by the United States Senate on February 24, 1806. In this role he swore in two Presidents of the United States, John Tyler and Millard Fillmore, each of whom assumed the presidency upon the death of his predecessor.
While serving as a Circuit judge, Cranch also served as the second reporter of the Supreme Court from 1801 to 1815. At the time, the reporter was an unofficial post and he used his own funds to produce the reports. Cranch took on the responsibility because of his respect for precedent. He was slow in producing his reports of cases and their accuracy was questioned.
During his tenure on the court, Cranch published a biography about Adams.
On February 3, 1826, the Columbian College board of trustees elected Cranch and William Thomas Carroll, Esq., as the first law professors. On June 13 of the same year, with President John Quincy Adams in attendance, Professor Cranch delivered the first law lecture in the court room of the City Hall. 
Cranch was elected a member of the American Antiquarian Society in 1813. During the 1820s, Cranch was a member of the prestigious society, Columbian Institute for the Promotion of Arts and Sciences, who counted among their members former presidents Andrew Jackson and John Quincy Adams and many prominent men of the day, including well-known representatives of the military, government service, medical and other professions.
Cranch is also known for several decisions that set a precedent for jury nullification (allowing a jury to nullify an "unjust" law and refuse to convict), including:
- United States v. Fenwick, 25 F. Cas. 1062; 4 Cranch C.C. 675 (1836): Right to make legal argument to jury.
- Stettinius v. United States, 22 F. Cas. 1322; 5 Cranch C.C. 573 (1839): Right to make legal argument to jury.
Cranch also handed down important precedent in a variety of topics, for example in a criminal law case regarding the mens rea of intoxication, Cranch wrote:
|“||It often happens that the prisoner seeks to palliate his crime by the pleas of intoxication; as if the voluntary abandonment of reason...were not, of itself, an offense sufficient to make him responsible for all of its consequences. ||”|
Cranch died in Washington, D.C., aged 86.
William Cranch's daughter Abigail Adams Cranch married William Greenleaf Eliot. William Eliot and Abigail Cranch were the parents of Henry Ware Eliot and the grandparents of T. S. Eliot. Cranch had four sons; of these three, Christopher, Edward, and John, all became painters.
- "Probing the Law School’s Past: 1821-1962". gwu.edu. Retrieved 4 May 2015.
- "MemberListC". American Antiquarian Society. Retrieved 4 May 2015.
- Rathbun, Richard. The Columbian institute for the promotion of arts and sciences: A Washington Society of 1816-1838. Bulletin of the United States National Museum, October 18, 1917. Retrieved 2010-06-20.
- William Cranch, White, Edward G. 1988. The Marshall Court and Cultural Change, 1815–1835. Vols. 3 and 4, History of the Supreme Court of the United States, 1815–1835. New York: Macmillan
- David Bernard Dearinger; National Academy of Design (U.S.) (2004). Paintings and Sculpture in the Collection of the National Academy of Design: 1826-1925. Hudson Hills. ISBN 978-1-55595-029-3.
- William Cranch at the Biographical Directory of Federal Judges, a public domain publication of the Federal Judicial Center.
- White, Edward G. 1988. The Marshall Court and Cultural Change, 1815–1835. Vols. 3 and 4, History of the Supreme Court of the United States, 1815–1835. New York: Macmillan.
- Witt, Elder. 1990. Guide to the U.S. Supreme Court. 2d ed. Washington, D.C.: Congressional Quarterly
Alexander J. Dallas
|Supreme Court of the United States Reporter of Decisions
1801 – 1815