The Twilight star has been awarded the title for the second year in a row in an annual poll by Britain's Glamour magazine.
She beat off stiff competition from fellow actress Emma Watson, who came in second, and the Duchess of Cambridge Kate Middleton, who took third place for her "sophisticated and demure outfit choices" and "unprecedented power to sell out high street garments".
Stewart was praised for her "personal rock-chick style" and daring red carpet looks.
Spider-Man star Emma Stone and country singer Taylor Swift rounded off the top five.
Also appearing the top 50 list are Keira Knightley, Kate Moss and the Duchess of Cambridge's sister Pippa Middleton.
Stewart takes best dressed title
Watson comes in second place
The Duchess of Cambridge takes third place
Emma Stone comes in fourth place in Glamour poll
Taylor Swift rounds off the top five