A lawyer by trade, Dorsey oversaw numerous education initiatives, vehemently opposed mob violence against blacks, and condemned the state's practice of a political convention system. While Dorsey tried with some success to bring Georgia into a more progressive era, he will forever be remembered as the man who prosecuted the notorious Leo Frank case.
He was born in Fayetteville on July 10, 1871, to Matilda Bennett and Rufus Thomas Dorsey, a prominent attorney. Dorsey attended Atlanta public schools as well as private schools in Atlanta and Hartwell. He studied at the University of Georgia in 1889-93 and at the University of Virginia law school in 1894. He returned to Atlanta the next year to practice law in his father's firm. In 1910 he was appointed solicitor general of the Atlanta Judicial Circuit, filling the unexpired term of Charles D. Hill. The following year Dorsey married Adair Wilkinson of Valdosta. The couple had two children.
In 1913 young mill worker Mary Phagan was found murdered in the basement of the Atlanta Pencil Factory, and her Jewish employer, Leo Frank, was accused of the crime. Dorsey's vigorous prosecution and subsequent success in the case won him favor with Watson. When outgoing governor John M. Slaton commuted Frank's sentence, protests erupted, led by Watson. A mob snatched Frank from his Milledgeville cell, carried him to Marietta, then lynched him and mutilated his body.
Dorsey, who was unknown until the Frank case, rode his newfound popularity to the gubernatorial race of 1916. At forty-five, Dorsey was the youngest man in the race, and he easily defeated incumbent Nat Harris and two other candidates. He was reelected in 1918 by a substantial margin. During his tenure the convention method of election was replaced statewide by the county unit system, which favored rural areas. Responding to the labor shortage due to World War I and the outmigration of blacks, the legislature passed a compulsory work law. Tax exemptions were granted for incorporated colleges, academies, seminaries, church property, public spaces, and charity institutions, and a board of public welfare was created to inspect jails and reformatories. In 1919 the legislature passed the most comprehensive school law to that date. Dorsey's initiatives began a drop in the illiteracy rate and established much-needed reforms for the state's lagging educational system.
In 1920 Dorsey ran for the U.S. Senate. More progressive than his opponent, especially over the question of race, Dorsey lost badly to Watson and returned to Atlanta to serve the remainder of his term as governor. Before leaving the office, however, he published a pamphlet entitled A Statement from Governor Hugh M. Dorsey as to the Negro in Georgia (1921) to be presented at a conference of citizens. In it he listed 135 examples of the alleged mistreatment of blacks in the state and suggested such remedies as compulsory education for both races, penalties to counties in which lynchings occurred, and a state commission to investigate those crimes. Historically an opponent of the mob violence that so stigmatized the South, he wrote, "To me it seems that we stand indicted as a people before the world."
Dorsey resumed his law practice after leaving office in 1921. Appointed judge of the city court of Atlanta in 1926, he was later elected to that position and served until 1935. He then became a superior court judge of the Atlanta Judicial Circuit. Dorsey died in Atlanta on June 11, 1948, and was buried in Westview Cemetery.