Munn said in an Instagram post on Sunday the girl was born via a surrogate on Thursday.
"I had so many profound emotions about not being able to carry my daughter," Munn said in the post that included a photo of the parents and baby together on a hospital bed.
"When I first met our gestational surrogate we spoke mother to mother. She showed me so much grace and understanding, I knew I had found a real-life angel. Words cannot express my gratitude that she kept our baby safe for 9 months and made our dreams come true."
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Munn added that "Méi (pronounced may) means plum in Chinese."
Mulaney, 42, and Munn, 44, who also share a two-year-old son, married in July.
Munn earlier this year revealed that she had been diagnosed with breast cancer and underwent a double mastectomy.
In an interview with People in March, Munn said Mulaney was by her side throughout and said it would have "felt like climbing an iceberg without him".
The two began dating in 2021 and welcomed their son, Malcolm, that November.
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