The couple, who are proud parents to their one-year-old son Sailor Gene, announced the happy news on Instagram.
Liv introduced her baby girl to the world with a photo of her cuddled up to her daddy.
"Hello!!!!! Our beautiful baby girl is here !!!!" she penned, revealing her little one's name, "Lula Rose Gardner we are sooooo happy heart exploding with love !!!!!"
This is the third child for Liv. The 38-year-old mum already has 11-year-old son, Milo, who she shares with her ex-husband, Royston Langdon.
Her fiance is also a dad to eight-year-old son, Grey, from a previous relationship.
Watch Liv talk about her pregnancy! Post continues...
The Leftovers starlet announced she was expecting in January.
"Oh my goodness it seems the stork is visiting us again!!!!" she shared alongside a black-and-white Instagram photo.
"I am growing another little Tyler Gardner in my belly. Our family is growing!!! So grateful. @davidgardner I love you."
Congratulations to the happy couple!