The 19-year-old star, best-known for her co-starring role as Hermione Granger in the six Harry Potter films released so far, has clinched the win with $5.4 billion in global box office receipts.
And her total will continue to tally when she appears in Harry Potter and the Deathly Hallows Parts 1 and 2, in 2010 and 2011 respectively.
Following Watson as the second top-earning actress was her Harry Potter co-star, British actress Dame Maggie Smith, whose films Gosford Park and The Divine Secrets of the Ya-Ya Sisterhood grossed $88 million (£55 million) and $74 million (£46.25 million) at the global box office respectively.