Swift grew up with Maack in Pennsylvania, and made time in her busy awards-season schedule to serve as Maack's maid of honor at the Saturday ceremony.
Swift told People she'd never been anyone's maid of honor before!
"This is my first time, and it's really, really important to me because this is my best friend, who I've known since I was born," she said.
In fact, Maack's new husband, Benjamin LaManna, is also someone both girls have known since they were small children.
Swift was a hands-on maid of honor — she went with Maack to Reem Acra's showroom over the summer to pick out dresses, an experience she tells People was "the best day ever."