His brothers were Oliver Hazard Perry Belmont and August Belmont, Junior. He attended Everest Military Academy in Hamden, Connecticut. And graduated from Harvard College in 1872.
Attended the law school in the University of Berlin.
And graduated from the Columbia Law School in 1876.
He was admitted to the bar that same year. Belmont practiced law in New York for five years. Elected as a Democrat to the 47th Congress and reelected to the next three Congresses, Belmont served as United States. Representative for the first district of New York from March 4, 1881 until his resignation on December 1, 1888.
The cross-examination concerned Blaine"s relations with a syndicate of American capitalists interested in the development of certain guano deposits in Peru.
An attempt was made to show that Blaine"s efforts toward mediation between Chile and Peru were from interested motives. Belmont served from 1885 to 1887 as chairman of the committee on foreign affairs
In 1898, during the Spanish–American War, Belmont served for six weeks in the Army as an Inspector General of the First Division, Second Army Corps, United States Volunteers, with the rank of major. He was appointed United States Minister to Spain that same year.
The marriage occurred only five hours after the divorce was decreed and, at the time, was considered scandalous.
In 1906, Belmont became "permanent president" of the National Publicity Bill Organization, which fought for campaign finance disclosure. During the First World War, despite being 65 years old, Belmont was commissioned as a captain in the United States. Army Quartermaster Corps on May 5, 1917. He was assigned to the Remount Division in Washington, District of Columbia and was discharged on May 21, 1920.
Through his mother he was a descendant of Captain Christopher Raymond Perry who had served as a privateer during the American Revolution.
Belmont died in Newport, Rhode Island on May 25, 1947 (age 95 years, 148 days). His former home in Washington, District of Columbia, became the International Temple for the Order of the Eastern Star.
During his first term, he was a member of the committee on foreign affairs Noted for his cross-examination of James G. Blaine, the former secretary of state. By virtue of his descent from Captain Perry, Belmont was a member of the Rhode Island Society of the Sons of the Revolution.
In 1929 he was elected an honorary member of the Rhode Island Society of the Cincinnati.
He was also a member of the Veteran Corps of Artillery.