Witherspoon announced the big news with a video of her floating by in a bikini, reminiscent of her character's law school application video.
The popular 2001 movie spawned a 2003 sequel and 2007 Tony-nominated musical. The plot of the third film has not yet been announced.
Since playing the unexpected law student, Witherspoon has gone on to found a production company, Hello Sunshine, dedicated to celebrating women's stories. She's also won an Oscar and an Emmy.