Ms Cooper will travel to the Big Apple next month, to help launch the ballet's United States tour.
She created garments and accessories for the company's ballerinas to wear at an opening night function, expected to be attended by celebrities, media and the who's who of international ballet.
Ms Cooper's centrepiece will be a one-off coat designed specially for Gillian Murphy, a principal dancer with the American Ballet Theatre and Royal New Zealand Ballet (RNZB).
Ms Murphy's fiance, Ethan Stiefel, became the RNZB's artistic director after retiring as a principal dancer with the American Ballet Theatre in 2012.
Ms Cooper said they were both extremely well-known in the US and it was a huge honour to create garments and accessories in association with them, as well as the RNZB.
The promotional value of launching her wares in New York at a formal gala was more than a Dunedin designer could hope for, she said.
It was believed to be the first time a designer had showcased their work with the RNZB on tour.
About 19 ballerinas would have Ms Cooper's clutches, handbags and other accessories at the ballet opening night after-party, on February 12.
The designer's relationship with the RNZB began in late 2008 when the company approached Ms Cooper to create a merchandise range, which she did under the label Tamsin Cooper.
''There were lots of synergies between the brands. Mine is quite theatrical and features luxury fabrics and silks as well as hand bead work, which is a nice match for the RNZB.''
Ms Cooper created a second range of merchandise under the label, and last year launched her own range of clothing and accessories inspired by the RNZB's 60th anniversary.
The collection, titled Anniversary, was revealed during the iD Dunedin Fashion Show, in which RNZB ballerinas joined models on the catwalk.
Ms Cooper said she was thrilled to be part of the ballet's US tour and hoped her working relationship with the company would develop.
''It's an amazing opportunity for a Dunedin designer,'' she said.
RNZB managing director Amanda Skoog said it made sense for New Zealand's creative companies to support each other on a world stage.
''Elegant design is integral to the ballet world and this is what makes our relationship with Tamsin Cooper such a natural fit.
''The dancers are delighted to be part of Tamsin's inspiration and to showcase her fashion items at our premiere in New York,'' she said.
