A rep for the actress confirms to PEOPLE that the couple welcomed their first child, a girl.
The announcement of the birth of their daughter comes a week after Sadoski revealed that he and Seyfried wed during a secret ceremony.
“I’ve never been excited by anything more in my life - and ready,” she recently told Vogue Australia about becoming a mother.
The new parents first met while working together on the off-Broadway show The Way We Get By in 2015, and began their romance when they reunited on the set of their upcoming film The Last Word. PEOPLE confirmed their relationship in March 2016.