"Carey has given birth to a healthy and happy baby," a source revealed. "She is just enjoying this time with her family and close friends."
The 30-year-old actress walked the red carpet for the first time on Wednesday since giving birth when she attended the British Film Institute's London Film Festival to promote her film Suffragette. Her husband is also keeping busy, preparing to resume his world tour with his band Mumford and Sons next month.
Mulligan and Mumford, who were childhood pen pals growing up, quietly wed on a farm in 2012. The couple announced they were expecting a child in June.