She and her twin sister, Ashley Olsen, were born June 13, 1986 in Sherman Oaks, CA to David and Jarnette Olsen. The twins began their acting career in 1987 when they were chosen to play the role of Michelle Tanner on a new series, "Full House." The show became a hit with books, dolls, and other merchandise being sold to promote it, and during the years the show was on the air, the Olsen twins became very popular.

The twins continued to share the role through the show's end in 1995.

Mary-Kate and Ashley teamed up with Robert Thorne and created Dualstar, their own production company. Soon after, they recorded an album titled Brother For Sale and a music video called Our First Video.

Later, they starred in the following Made For TV Movies: To Grandmother's House We Go (1992) (TV), Double, Double, Toil and Trouble (1993) (TV), and How the West Was Fun (1994) (TV).

They also created their own video series called The Adventures of Mary-Kate and Ashley, in which they were pint size detectives who would "solve any crime by dinner time." They also have another successful video series, You're Invited to Mary-Kate and Ashley's and both video series continue to be popular today. In 1995 they made their big screen debut in It Takes Two (1995) and in the next few years they continued to make videos in their series. In 1998 they returned to television in the short lived series, "Two of a Kind" (1998).