The `Little Miss Sunshine` actress - who already has a three-year-old daughter Sage with husband David Galafassi - gave birth to a baby boy in her native Australia.
The couple have named their new arrival Arlo Robert Galafassi and both mother and son are doing well.
Her representative told People: "ToniCollette, her husband David Galafassi and their daughter Sage Galafassi are excited and proud to announce the arrival of their baby boy, Arlo Robert Galafassi. He was born on Good Friday making it the greatest Friday, indeed!"
Toni and David - who married in 2003 - have homes in both Australia and Ireland and split their time between the two.
While Toni is celebrating the safe arrival of baby Arlo, she recently revealed she is terrified of dying because she worries about what will happen to her friends and family when she has gone.
She said: "I think about it a lot, you know, what`s going to happen. I guess it`s the fact that I won`t exist and I won`t be around people that I love. I suppose my worst fear is that I don`t know what happens afterwards - it`s the ultimate unknown.
"I think the nearer I get - and I am getting closer to it, I accept that - it doesn`t make me freak out so much anymore. But I think the sooner I fully accept it, the sooner I will fully immerse myself in life."