The 27-year-old actress, who has been dating Charlie McDowell since 2010, was spotted wearing an unusual diamond ring on her engagement finger while enjoying a lunch date with her director beau in New York, reported Daily Mail online.
This is the first time the Oscar nominated star has been photographed with the ring in public.
The actress has always been tight-lipped about her relationship with Charlie, who comes from a famous family.
His parents are Malcolm McDowell and Mary Steenburgen, his stepfather is Ted Danson, and his sister is 'Sons of Anarchy' actress Lily McDowell.
Despite her success on the big screen, Rooney has previously insisted she isn't comfortable in the spotlight.
She said that she finds it 'annoying' people want to know what she's wearing and would rather they concentrate on her acting skills rather than her fashion sense.