Background, family, and early life
Fish was born Hamilton Stuyvesant Fish in Garrison, New York to the former Republican U.S. Representative Hamilton Fish II and the former Emily Mann. His paternal grandfather, Hamilton Fish, was United States Secretary of State under the Republican President Ulysses S. Grant. The father of the first Hamilton Fish, Nicholas Fish (born 1758), was an officer in the Continental Army and was later appointed adjutant general of New York by Governor George Clinton.
The wife of Nicholas Fish was Elizabeth Stuyvesant, a descendant of Peter Stuyvesant, who was the Dutch colonial governor of New York. Through his mother, Emily Mann, Hamilton Fish III was also a descendant of Thomas Hooker, who settled Hartford, Connecticut in 1636. Fish's uncle Elias Mann was a judge and three-term mayor of Troy, New York.
Fish's great-grandmother, Susan Livingston, married Count Julian Ursyn Niemcewicz in 1800 after the death of her husband, John Kean (who had been a delegate to the Continental Congress from South Carolina.) A soldier and statesman, Niemcewicz was credited with writing the Polish Constitution of 1791. John Kean and Susan Livingston's great-grandson, and thus a relative of Fish, was Thomas Kean, who was elected governor of New Jersey in 1982.
A cousin of Hamilton Fish III (also named Hamilton Fish) was a sergeant in Company L of Theodore Roosevelt's "Rough Riders", and the first American soldier killed in action during the Spanish–American War. Hamilton Fish II had his ten year-old son's name legally changed from Hamilton Stuyvesant Fish to just Hamilton Fish to honor his fallen cousin (he and Hamilton Fish III never met).
Fish was married in 1921 to Grace Chapin Rogers (1885–1960), daughter of onetime Brooklyn Mayor Alfred C. Chapin (1848–1936). Their son, Hamilton Fish IV, was a thirteen-term U.S. Representative from New York, holding office from 1969 to 1995. The Fishes' daughter Lillian Veronica Fish married David Whitmire Hearst, son of William Randolph Hearst.
During his childhood, Fish attended Chateau de Lancy, a Swiss school near Geneva, which his father also attended in 1860; there, the younger Fish learned French and played soccer. He spent summers with his family in Bavaria. He began his U.S. boarding school education at Fay School in Southborough, Massachusetts, and he later attended St. Mark's School, a preparatory school also in Southborough. Fish later described himself as a "B student" but successful in several different sports.
Graduating from St. Mark's in 1906, Fish went on to attend Harvard College, class of 1910. There, he played on Harvard's team as a tackle and was a member of the Porcellian Club. Standing 6 feet 4 inches (1.93 m) and weighing 200 pounds (91 kg), "Ham" Fish was highly successful as a football player; he was twice an and in 1954 was inducted into the . He was the only Harvard man on Yale graduate Walter Camp's "All time" "All America" team. After graduating from Harvard, Fish continued his involvement in football. He donated $5000 for several awards to Harvard football players; and organized the Harvard Law School football team, which played exhibition games with other colleges around the country.
In 1909, aged twenty, Fish graduated early from Harvard with a cum laude degree in history and government. He declined an offer to teach history at Harvard and instead attended Harvard Law School. He left law school before graduating, and took a job in a New York City insurance office.
Fish was a Progressive member of the New York State Assembly (Putnam Co.) in 1914, 1915 and 1916.