Allen, Charles was born on April 17, 1827 in Greenfield, Massachusetts, United States. Son of Sylvester and Harriet (Ripley) Allen.
Allen graduated from Harvard University in 1847, studied law, and was admitted to the bar in 1850.
Allen practiced law at Greenfield for twelve years, then advanced to state offices, serving as the Massachusetts Attorney General from 1867 to 1872. During his sixteen years of service (1882–1898) on the bench of the Massachusetts Supreme Judicial Court, Allen became known as one of the most eminent jurists of his day.