Spelling gave birth to daughter Hattie Margaret McDermott on Monday.
The couple confirmed the news over their Twitter accounts, saying the baby is "gorgeous" and the family is "so happy."
Spelling and McDermott already have two children together, Liam and Stella. McDermott also has a son from a previous marriage.
The birth was first reported by Life & Style magazine.
Spelling wed McDermott in 2006 after meeting on the set of a TV movie.
The couple plans to introduce their new baby on the premiere of the sixth season of their reality show, "Tori & Dean: Home Sweet Hollywood." It airs Nov. 29 at 10pm ET/PT on Oxygen.