The engagement comes days after former "Mad Men" cast member Jared Harris proposed to Allegra Riggio, People reported.
"I was surprised that it was happening at that moment," Cardellini, 37, said on Friday's episode of The View, of the proposal. "We were actually with some of the people I love most: my sister, and my cousins and one of my best friends Maura [Tierney] ... and we were sitting, and he started getting choked up and then got on his knee. It was very beautiful."
Cardellini and Rodriguez have a daughter together, Lilah-Rose, who was born in February 2012.