Sydney Francis Foster was born in Cazenovia, New York on March 23, 1893, the son of a farmer. He attended Cazenovia Seminary and Syracuse University, and in 1915 was awarded his law degree from Syracuse University Law School. He then accepted a position as Deputy County Clerk in Madison County, where he served from 1916 to 1918, having been admitted to the Bar in 1917. When World War I broke out, Foster enlisted in the American Expeditionary Forces, serving in the Judge Advocate General Unit in France.
After completing his military service in 1920, Foster moved to Sullivan County where he joined the law office of Joseph Rosch. Five years later he was elected District Attorney of Sullivan County and served until his election to the Supreme Court, 3rd Judicial District in 1928. While serving on the Supreme Court in Greene County, he presided over the criminal trial of Manning Strewl, who had been charged with kidnapping the nephew of an Albany political leader. In 1937 Judge Foster sentenced Strewl to 15 years after he pleaded guilty to blackmail as a substitute for the 50-year term imposed on him earlier for the abduction.
Governor Lehman designated Foster to the Appellate Division Third Department in 1939, where he served until the end of 1942, at which time he returned to the trial bench. He was again designated to the Appellate Division Third Department, this time by Governor Dewey, in 1944. Dewey also appointed him Presiding Justice in 1949, serving until 1960. From 1952 to 1953, Foster was at various times temporarily designated to the Appellate Division First Department. In 1954 he first ran for the Court of Appeals but was defeated by Judge Adrian Burke. Governor Rockefeller subsequently appointed Foster to the Court of Appeals in 1960 to fill a vacancy. He was elected to the Court later that year.
When he was Presiding Justice of the Appellate Division, Third Department Judge Foster wrote the minority opinion when the court upheld a ban on "La Ronde," a French film that the Board of Regents had banned as immoral. He held that consorship was "an infringement upon freedom of expression." However, ten years later, as a member of the Court of Appeals he concurred with the majority when the Court ruled that the book "Tropic of Cancer" was obscene under New York's obscenity laws.
He retired from the Court of Appeals in 1963 at the mandatory retirement age of 70, returning to the Supreme Court as a certificated trial justice for four more years.
Judge Foster married Mabel Angel Foster in 1924, with whom he had one child. He passed away on November 21, 1973 at age 80.
Bernard S. Meyer, Burton C. Agata & Seth H. Agata, The History of the New York Court of Appeals, 1932-2003, Columbia University Press, New York, 2006, pp. 24-25.
The Judges of the New York Court of Appeals, A Biographical History, Albert M. Rosenblatt [ed.], The Historical Society of the Courts of the State of New York, New York, 2007, pp. 647-651.
Obituary, New York Times, November 23, 1973, p. 38.