"The baby is healthy," the source tells Us. "They have been loving being parents and their friends and family are thrilled."
Us broke the news in June that the British actress, 30, was pregnant. That same month, she showed off her growing baby bump in a maroon-colored strapless gown while attending the 2015 Tony Awards in NYC.
On Wednesday, Oct. 7, Mulligan made her first red carpet appearance since giving birth at the British Film Institute's London Film Festival. She wore a baggy top and a colorful knee-length skirt.
The Walker actress and the Mumford & Sons frontman, 28, were previously childhood pen pals before their friendship blossomed into romance in 2011. As Us exclusively reported, they tied the knot in Somerset, England, in April 2012. Famous pals such as Jake Gyllenhaal, Sienna Miller, and Colin Firth were in attendance.
"They're a great couple," an insider previously told Us. "Very sweet."
E! was first to break the baby news.
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