The couple have a 1-year-old son together and Ainsley is pregnant with their second child.
Ritchie also has two sons with his ex-wife, U.S. pop star Madonna.
"They're over the moon in love," an insider told People.com about Ritchie and Ainsley.
Ritchie's films include "Sherlock Holmes," "Snatch" and "Lock, Stock and Two Smoking Barrels."
Celebrity Breakups and divorces of 2014 [PHOTOS]