Johnson's fashion career started after she entered and won the Mademoiselle Guest Editor Contest. Within a year, she was the in-house designer for Manhattan boutique Paraphernalia. Johnson became part of both the youthquake fashion movement and Andy Warhol's underground scene, along with The Velvet Underground, Edie Sedgwick, Nico, and Lou Reed. In 1969, she opened a boutique called Betsey Bunky Nini on New York City's Upper East Side. Edie Sedgwick was her house model and Johnson designed the clothing Sedgwick wore on her last film, Ciao! Manhattan.