Dressed in form-fitting workout wear, the actress, 29, stepped out in New York City on Wednesday with her fiancé, French journalist Romain Dauriac.
The outing marked the first public sighting of the couple since they announced last month's arrival of their first child, daughter Rose Dorothy.
The ultra-private actress quietly revealed her engagement last September after sporting a stunning vintage Art Deco-style ring at the Venice International Film Festival.
On Wednesday, it was Dauriac's turn to raise eyebrows, with a new gold band on his left ring finger.
Which makes us wonder … did the new parents secretly tie the knot? Johansson's rep has yet to respond for comment.