The ad, called "music that moves", launched yesterday online and on TV in the US during 'American Idol'.
The 30-second spot by Droga5 is the first by the brand to feature Swift and was shot in her home town, Nashville. It features the pop star penning her song '22'.
The work was created by copywriter Sophie Isherwood and art director Andrew Wilcox. It was directed by Fredik Bond through production company, MJZ and the executive creative directors were Ted Royer and Nik Studzinki.
Diet Coke celebrates its 30th anniversary in the UK and Europe this year. The brand is putting the occasion at the heart of its marketing, to engage with its core female target audience in the aftermath of the Olympic Games.