James Samuel Watson was born in Spanish Town on May 29, 1882. His father, James Michael Watson was a Sergeant in the Jamaica Constabulary Force and later worked for the Jamaica Government Railway, as a conductor and platform foreman. His mother was Elizabeth Jones Watson, but there seems to be no further information about his parents, such as what part of Jamaica they originally came from. Several sources mention a family relationship to the families of Colin Powell and Bruce Llewellyn, but that connection may be through Violet Lopez, James S Watson's wife. He received his early education in Jamaica, presumably in elementary schools in Spanish Town. After leaving school he worked at the Myrtle Bank and Constant Spring Hotels, as bookkeeper, cashier and chief clerk.
In June 1905 he arrived in New York, and spent much of his time over the next five years advancing his education at the New York, and Harlem, Evening High Schools, receiving a general diploma in 1910. For the next three years he went to evening sessions at City College and at the same time worked for his law degree at the New York Law School, receiving the LL.B in 1913. From 1908 to 1914 he was a law clerk at House, Grossman and Vorhaus, at 115 Broadway. He was admiited to the New York State Bar in April 1914, and in May to practise in the US District Court, Southern District of New York. He remained at House, Grossman and Vorhaus until 1920, becoming head of their Department of Corporate and Tax Law.
In 1920 he started his own law firm, joined by two Black attorneys, S T Christian, and J E Stevens. From 1922 to 1930 he worked as Special Assistant Corporation Counsel of the City of New York in the Special Franchise Tax Division. In 1930, having successfully campaigned to become a Municipal Court judge along with running mate Charles E. Toney, and thus becoming one of the first two justices of African descent elected to judicial office in New York City, he handed his law firm over to his two colleagues.
James S Watson served as Municipal Court Judge from 1930 to 1950, winning re-election in a bitter campaign in 1940, when a committee including Adam Clayton Powell Jr had to put pressure on the local Democratic political machine to support his candidacy.
In May 1950 he resigned from his judicial post in order to accept the presidency of the Municipal Civil Service Commission, a position he still held at the time of his death 2 years later.
The constant themes of references to the legal career of James S Watson are his wide legal knowledge and his scrupulous fairness, which won him the respect of his legal colleagues and the public at large. In 1934 a Jamaican returning to the island from the USA told an audience that 'it would not be long before Judge Watson would be appointed to the United States Supreme Court.'