During the graduation ceremony the actress was accompanied by an undercover armed guard, contradicting statements the star has made about having a ‘normal’ student experience.
The policewoman wore a cap and gown to blend in with the hundreds of graduating students.
Despite taking time out to star in a number of films, Watson graduated with a bachelor's degree in English literature from the Ivy League university.
Watson, who also studied at Oxford University, tweeted a photograph of herself in cap and gown, with a single exclamation mark as the caption.
Despite finding fame at a young age when she starred in the hugely successful Harry Potter films, the star was a model student at school in the UK, scoring a clean sweep of As in her GCSE and A-level exams.
The actress began her studies at Brown in 2009, the same year she was named the highest-grossing actress of the decade by the Guinness Book of World Records.
In 2011 the star went to Oxford University as a visiting student to read English at Worcester College.
While studying Watson managed to act in both parts of Harry Potter And The Deathly Hallows, The Perks Of Being A Wallflower and This Is The End.