Born in San Rafael, California into a family that was allegedly descended from one of the earliest Spanish families to settle in California, Marin Sais began her acting career as a teenager after travelling to New York City where she appeared in vaudeville.

In 1910, at the age of twenty, Sais made her screen debut for New York City's Vitagraph Studios in the short film adaptation of William Shakespeare's Twelfth Night opposite the notable actors Florence Turner and Julia Swayne Gordon. Sais would go on to star in a number of well-received comedy shorts for Kalem Company opposite actors Ruth Roland, Marshall Neilan and Edward Coxen. In 1911, Sais made her first appearance in a Western entitled The Ranger's Stratagem - it would become a frequent career choice for the actress and in her later career she would rarely appear in other motion picture genres.

Throughout the 1910s, Sais' career as an actress continued to build momentum and the actress showed her versatility by appearing in such varied genres as comedy shorts, Westerns, dramas, and beginning in 1915 she began appearing in a James W. Horne directed Kalem Company Nancy Drew-style mystery serial The Girl Detective, with such titles as: The Riddle of the Rings, The Secret Code, The Disappearing Necklace and The Vanishing Vases. Sais also continued to work under the direction of Horne in dozens of Western shorts. In 1916 she began appearing as the character Barbara Brent in a Horne directed Western series of shorts.

By 1918 Sais was a highly popular and publicly recognizable film personality and was chosen by Japanese silent film matinee idol Sessue Hayakawa to appear opposite him in a series of film collaborations, the first being 1918's The City of Dim Faces.

In 1920, Sais married silent Western actor Jack Hoxie who she met on the set of the 1916 film Tigers Unchained and the two began appearing in a number of well-received Western action and adventure films. Although the couple would divorce seven years later, Sais would rarely appear in in films outside of the Western genre from 1920 onward. One notable film of the period was the Bruce M. Mitchell directed 1924 film The Hellion, which featured British actor Boris Karloff in one of his first prominent roles.

By the mid-1920s Marin Sais' career was declining and she began appearing in a number of lower budget Westerns. It was a trend that would follow Sais throughout her career into the talkie era of the 1930s and give her the dubious title of "Queen of the B-movie oaters". During the 1930s, Sais appeared in approximately twenty films - all Westerns except for an uncredited role as Mrs. Harper in 1936 cult classic Reefer Madness.

Sais' acting career continued throughout the 1940s and into the 1950s, often in bit parts or in uncredited roles in poorly recieved, low budget Westerns. Two exceptions were the popular 1945 Sam Newfield directed Western Lightning Raiders, starring Buster Crabbe and her role as The Duchess in the long-running 1949 Red Ryder serials starring Jim Bannon. By the early 1950s, she made a tentative foray into the new medium of television with guest a appearance on The Lone Ranger. Sais' last role before retirement was a small part in the made-for-tv movie The Great Jesse James Raid in 1953.

In her later years, Marin Sais retired to the Motion Picture & Television Country House and Hospital in Woodland Hills, California where she was a resident for many years. She died in 1971 of cerebral arteriosclerosis at the age of 81.