The Disobedience star, 39, was photographed with Linden, 38, for the first time since they welcomed a son together in April.
The two enjoyed a laid-back lunch in Los Angeles with the actress wearing a white T-shirt, gray leggings, gray sweater and sneakers as Linden also dressed casually in blue jeans, white T-shirt, gray cardigan and baseball cap.
McAdams was photographed in early April walking beside Lindon, who appeared to be carrying a newborn baby in his arms.
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The couple was first romantically linked in April 2016 and kept a relatively low profile throughout their relationship.
McAdams made her first red carpet appearance since welcoming her son in late April while promoting her film Disobedience.
RELATED VIDEO: Rachel McAdams Welcomes a Son with Boyfriend Jamie Linden: Report
While the actress has not confirmed the news, E! News first revealed she was pregnant in February.
Her costar Rachel Weisz told the outlet McAdams was happier than ever.
“She is just glowing and looking ravishing and gorgeous,” Weisz told E! News. “She just seems to be so happy and I am just so happy for her! She had her first baby—it’s so beautiful!”