Hart gave birth to Mason Walter Wilkerson in Los Angeles late Wednesday afternoon, People magazine reported.
The 9-pound bundle of joy is the first child for Hart, 29, and her husband, Mark Wilkerson, 28.
"He was a little stubborn, but all is well," Hart told People. "Everyone is well and we are all relieved."
Hart has described her meeting with Wilkerson as "love at first sight."
They met when she introduced his band, Course of Nature, at the 2002 Kentucky Derby's Mint Jubilee cancer fundraiser.
Their 2003 wedding in Florence, Italy, was documented in a six-part ABC series, "Tying the Knot: The Wedding of Melissa Joan Hart."