Milton Sills was born in Chicago, Illinois into a wealthy and highly regarded family. He was the son of a successful mineral dealer father and an heiress mother from a prosperous banking family. Upon completing high school, Sills was offered a one-year scholarship to the University of Chicago where he studied psychology and philosophy. After graduating, he was offered a position at the university as a researcher and within several years worked his way up to becoming a professor at the school.
In 1905, stage actor Donald Robertson visited the school to lecture on author and playwright Henrik Ibsen and suggested to Sills that he should try his hand at acting. On a whim, Sills agreed and left his prestigious teaching career to embark on a stint in acting. Sills joined Robertson's stock theater company and began touring the country.
In 1908, while Milton Sills was performing in New York City, he garnered critical praise from such notable Broadway producers as David Belasco and Charles Frohman. That same year he made his Broadway debut in This Woman and This Man, which was an immediate success with both the theater-going public and critics. From 1908 to 1914, Sills appeared in about a dozen Broadway shows, becoming a crowd favorite and attaining a great deal of fame.
In 1910, Sills married English stage actress Gladys Edith Wynne, a niece of actress Edith Wynne Matthison. The union produced one child, Dorothy Sills, and the couple divorced in 1925. In 1926, Sills remarried, this time to silent film actress Doris Kenyon, and the couple had a son, Kenyon Clarence Sills, born in 1927.
In 1914, Milton Sills decided to conquer the new medium of motion pictures. He made his film debut the same year in the big-budget drama The Pit for World Company studios and was signed to a contract with film producer William A. Brady. The film was enormously successful and Sills made three more films for the company, including another huge box-office draw The Deep Purple opposite silent screen star Clara Kimball Young. By the late 1910s, Sills had reached leading man status and parted ways with the relatively small World Film company, taking the then unusual path of freelancing as an actor.
By the early 1920s, Sills was enjoying a highly successful acting career and working for such prominent film studios as MGM, Paramount Pictures, and Pathé. Sills was often paired with the most popular leading ladies of the era, including: Geraldine Farrar, Gloria Swanson and Viola Dana. His greatest public and commercial successes came with the now-lost Flaming Youth (1923) opposite Colleen Moore, and the enormous box-office hit The Sea Hawk (1924).
On May 11, 1927, Sills had the distinction of being among the original 36 individuals in the film industry to found the Academy of Motion Picture Arts and Sciences (AMPAS), a professional honorary organization dedicated to the advancement of the arts and sciences of motion pictures. Fellow performers included: Mary Pickford, Richard Barthelmess, Jack Holt, Conrad Nagel, Douglas Fairbanks, and Harold Lloyd.
Sills' last work was not The Sea Wolf (1930) but a book published posthumously in 1932: Values: A Philosophy of Human Needs - Six Dialogues on Subjects from Reality to Immortality - co-edited by Ernest Holmes. Milton Sills was an unusual blend of actor and academic.
Milton Sills made two sound pictures, showing that he had an excellent voice. He died unexpectedly of a heart attack in 1930 while playing tennis with his wife at his Santa Barbara, California home at the age of 48. He was interred at the Rosehill Cemetery and Mausoleum in Chicago, Illinois.
For his contribution to the motion picture industry, Milton Sills was awarded a star on the legendary Hollywood Walk of Fame at 6263 Hollywood Blvd. in Hollywood, California.