James S. Watson was born in Spanish Town, Jamaica, West Indies on May 29, 1882, the son of Elizabeth Jones Watson and James Michael Watson, a Sargeant of the Jamaica Constabulary and Dispatcher of the Jamaica Railway Compan. He received his education in the public schools of Jamaica and after graduation was employed in the hotel industry. He was bookkeeper, chief clerk and cashier at the Myrtle Bank and Constant Spring Hotels respectively, two of the largest hotels in the island.

In June of 1905 Watson immigrated to the United States. From 1905 to 1910 he attended New York Evening High and Harlem Evening High schools from which he received a diploma upon completion of a five-year General course. From the Fall of 1910 until 1913 Watson attended evening sessions at The City College of New York; during the same period he attended New York Law School from which he received the LL.B. in 1913. He was admitted to the New York State Bar on April 6, 1914 and admitted to practice, United States District Court, Southern District of New York, May 1, 1914.

Watson received his practical law training and experience in the law offices of House, Grossman & Vorhaus at 115 Broadway where he was employed in various capacities from 1908 to 1920. From 1908 to 1914 he was a law clerk and later as a member of the legal staff he headed the firm's Department of Corporation and Tax Laws, a position he occupied until March of 1920. In the same year he opened his own law practice at 240 Broadway, specializing in corporate, contract and tax law. From 1922 to December 31, 1930 Watson was Special Assistant Corporation Counsel of the City of New York in the Special Franchise Tax Division. While serving in this capacity his private practice was handled mainly by two black Attorneys, Sidney T. Christian and John E. Stevens; on December 31, 1930 he turned the practice over to Messrs. Christian and Stevens who later formed a partnership.

Watson successfully campaigned for Municipal Court judge in 1930 and along with running mate Charles E. Toney became one of the first two justices of African descent elected to judicial office in New York City. At the time a member of the Cayuga Democratic Club and the United Colored Democracy, Watson was designated to run in the newly-created Tenth Municipal District. This District which was bordered by 110th Street to 155th Street and St. Nicholas Avenue to Fifth Avenue was created in 1929, after much agitation, to assure the election of judiciary candidates of African descent. Watson and Toney won by a landslide beating out Republican opponents Francis E. Rivers and John C. Hawkins in what was then a heavily Republican district. Watson was inducted on January 1, 1931.

The Municipal Court, also known as the “poor people's court,” decided tenant and landlord cases and small civil cases in general. The new Tenth District Municipal Court was especially heavy in tenant-landlord cases and had experienced a large increase in such cases by 1931 due to rising unemployment caused by the Depression. Initially Watson held court in the Municipal Court's temporary quarters at 125th Street and Fifth Avenue, but owing to the Municipal Court Code he rotated within the Borough of Manhattan and in emergencies also held court in Brooklyn and the Bronx. In Brooklyn, Watson became the first justice of African descent to sit in judgement over white litigants. In 1932 he substituted in the Bronx and his services were so highly thought of that the Bronx County Bar Association officially requested an extension of his time, not only out of necessity but because his work was so highly acclaimed. According to some sources, during his first 196 days on the bench, Justice Watson heard 1,080 inquests, 896 non-jury trials, 123 jury trials, 2,381 motions, 4,294 summary proceedings and 2 ex-parte actions. One source reports that by 1937 the Appellate Division had upheld him in 157 cases and only reversed him in 93.

In 1940 Watson and Toney ran for re-election. While Toney was again designated as a candidate by the Democratic Party, Watson, despite the unanimous endorsement of the Association of the Bar of the City of New York and the New York County Lawyers Association was denied re-designation by local Democratic leader Danny Burrowes in favor of Vernon J. Reddick, an Assistant Attorney General. Concerned supporters formed The Citizens' Non-Partisan Committee to Re-Elect James S. Watson headed by George Gordon Battle as the citywide chairman and Adam Clayton Powell, Jr. as co-chair and chairman of the Harlem Division. Scores of lawyers of varied political affiliation were members of the Committee and there was also a physicians' and dentists' division. Watson ran as an independent candidate but was endorsed by the American Labor Party. Under pressure, Tammany Hall eventually backed Watson, overriding the decision of local Democratic leaders. Watson was nominated in the Primary, Reddick withdrew and Independent opponent Richard E. Carey placed third. Watson won the election by the majority of votes in what was said to be a record-breaking re-election, running ahead of the entire Democratic ticket by 9-to-1.

In May 1950 Watson resigned his position in the Municipal Court to accept the presidency of the Municipal Civil Service Commission, a post previously held by Ferdinand Q. Morton. The Commission's responsibilities included administering the civil service examination and recruiting qualified personnel for all departments of the city government. Under Watson's brief leadership the Commission was able to replace a large number of provisional employees with permanent personnel. He also won all legal actions brought against the Commission. In October of the same year, former Municipal Court Justice Nathan Sweedler tendered a luncheon in Watson's honor in a tribute to his services and contributions to the legal community and in the spirit of interracial fellowship.

Watson was considered one of the most able jurists in New York and was one of the most popular judges on the bench. Known for his learned ability and fairness, he was lauded by the legal community and the public alike. He was a member of the Rules Committee and the Landlord and Tenant Committee, both of the Municipal Court. Several of his decisions have made history in the annals of law. Chief among them is his ruling in Perry v. Norddeutscher Lloyd (North German Lloyd Steamship Company) which was upheld by the higher court. In a 1934 decision, Watson ruled that the moratorium decree of the German government was not binding on persons owning bonds of German corporations issued in the United States and payable in dollars. The company in question was therefore obliged to pay the bondholder the semiannual interest accrued. Some other outstanding decisions rendered by Watson include National Surety Corporation v. Federal Reserve and Nickobon, Inc. v. Ross. In recognition of his impressive public service record he was honored by a testimonial dinner in 1938, sponsored by the Bar Association of the City of New York. More than 500 persons attended and those paying tribute included Sir Gerald Campbell, British Counsel General, Lester A. Walton, United States Minister to Liberia and Pelham St. George Bissell the President-Justice of the Municipal Court of the City of New York. At times Watson was suggested for higher office and in 1949 he was recommended to President Truman for a federal judgeship in the United States District Court of New York; he was also recommended to the Department of the Interior for the post of Governor of the Virgin Islands. Watson received honorary doctorates from Shaw University, Raleigh, North Carolina and Lincoln University, Pennsylvania.

Watson was active in various professional associations and in 1943 was the first attorney of African descent nominated to the American Bar Association since 1912. He also held membership in the Association of the Bar of the City of New York, the New York County Lawyers Association, on whose Administrative Law and Civil Rights Committees he served, the Harlem Lawyers Association and the National Bar Association of which he was a one-time Regional Director. He also lectured at the Practicing Law Institute in New York City in post-admission education for lawyers.

Watson also played an active part in civic and community affairs and was a member of various civic, fraternal and charitable organizations. Memberships included the New York Urban League, Grand Street Boys' Association, the Grand Street Boys' Foundation, Alpha Phi Alpha Fraternity and the Prince Hall Masons. His favorite charities were the Hope Day Nursery in Harlem, Forrest Neighborhood House, Bronx, New York and the Wiltwyck School for Boys, Inc. He was charter member of St. Martin's Episcopal Church in Harlem and served as Junior Warden and on the Vestry. He was a frequent guest speaker for religious, civic, fraternal, social, educational and legal organizations and was once quoted as saying, “It is my conviction that the appearance of a Negro judge can be most encouraging to members of our race, young as well as old.” He strongly believed that those elected to public office should participate in such activities as an example of service and inspiration to youth. His concern with juvenile problems led him to readily lecture before school, Sunday school and youth groups. He also served as a member of the Board of Managers of the Young Men's Christian Association in addition to participating in other community activities concerning juvenile issues.

Watson was equally interested in race-related matters and believed in the solidarity of native born and foreign born peoples of African descent in finding a solution to common problems. During the 1939 World's Fair, Watson rejected the command invitation of the King and Queen of England to attend the fair because he strongly believed that members of the African-American community should also have been invited to participate in the celebration. Watson often spoke before groups of various ethnic backgrounds and was elected to honorary membership in the Free Sons of Israel. As a member of the West Indian community he was held in high esteem by his fellow Islanders. He frequently spoke to different groups, oftentimes traveling to other cities. From 1919 to 1930 he represented West Indians from various islands, particularly Jamaica, at the request of the British Consulate. For this and other work he was appointed Commander of the Most Excellent Order of the British Empire. He also incorporated and represented various organizations and held membership in a few such as the British Jamaicans Benevolent Association.

Watson was a family-oriented man and often credited his wife Violet Mae (nee Lopez), a fellow Jamaican, with much of his success. The two met in the United States and were married in 1917. This union produced four offspring, two boys and two girls. The eldest, Barbara, was a former United States Ambassador to Malaysia and the youngest, James is a former New York State Senator now with the United States Court of International Trade.

On May 9, 1952 after a brief illness, James S. Watson died at his home at 117 West 120th Street, in Harlem. Funeral services were held at St. Martin's Church with internment in Woodlawn Cemetery, Bronx, New York. It is estimated that over 3,000 mourners attended the services alone, while over an additional 7,000 viewed the procession. The list of honorary pallbearers, headed by Mayor Vincent R. Impelliteri, included virtually every high-ranking city official and civic leader.