The new couple smooched at midnight in New York's Times Square – a romantic moment now being shared by millions thanks to a bystander's fuzzy photo sweeping the Internet.
Just before Christmas, Swift, 23, spent a ski vacation with the 18-year-old One Direction singer, along with pals Justin Bieber and Selena Gomez.
On Monday night, Swift performed "I Knew You Were Trouble" and "We Are Never Ever Getting Back Together" on Dick Clark's New Year's Rockin' Eve with Ryan Seacrest before stealing the kiss with Styles.
A fan of the number 13 – her Twitter handle is @TaylorSwift13 – she also told her followers that she's looking forward to 2013: "There are 13's EVERYWHERE. This is PERFECT."