Mix sugar, margarine, and evaporated milk in a large, heavy saucepan over medium heat, stirring to dissolve sugar. Bring mixture to a full boil for 5 minutes, stirring constantly.
Remove from heat and stir in chocolate chips until melted and thoroughly combined. Beat in marshmallow creme, walnuts, and vanilla extract.
Transfer fudge to the prepared pan and let cool before cutting into squares.
