The girls were born in Sherman Oaks, California to David Olsen (b. 1953) and Jarnette (Jarnie) Fuller (b. 1954) in 1986. Mary-Kate and Ashley Fuller Olsen started their acting careers on the television series Full House in 1987. They were hired at the age of six months and filming began when they were nine months old. The show was widely popular during the late 1980s and early 1990s. Both sisters played the same character, Michelle Tanner, taking turns during the tapings to do so, in order to comply with strict child labor laws regarding child actors. For the first year, Ashley would cry when she was brought on set to do a scene, so Mary-Kate had more screen time in the first season.

Because the producers did not want viewers to know that Michelle was played by twins, the sisters were originally credited as "Mary Kate Ashley Olsen", but in the last season and most of season one, they were credited as separate people. During the eight year run, Mary-Kate and Ashley made several