The 21-year-old actress joined the star in his dressing room after watching him perform in How To Succeed In Business Without Really Trying at the Al Hirschfeld Theatre in New York City.
The pair, who are clearly close after their many years on the set of the hit wizard franchise, hugged affectionately as they posed for the camera.
She has previously described their relationship as 'like brother and sister'.
Surprise! Emma Watson joined Daniel Radcliffe backstage at How To Succeed in Business Without Really Trying in New York last night
'What's great about the part is that the stuff he does is pretty unpleasant,' said Daniel. 'He gets people fired, but you love him for some reason.'
'You believe in him and want him to succeed and it's great fun.'
Daniel had singing lessons for his musical debut on the Broadway stage, which has largely won good reviews.
Co-stars: The pair with Rupert Grint in the upcoming film, Harry Potter and the Deathly Hallows - Part 2
The pair will soon hit the promotional trail to coincide with the release of Harry Potter and the Deathly Hallows: Part 2 in July.
It is the final part of the saga and the actress has admitted she was 'devastated' when the finished shooting for the very last time.
Acclaim: The actor soaks up the applause on the first night of Broadway Play How to Succeed in Business Without Really Trying last month