Trelise Cooper is one of New Zealand's most successful and internationally recognised fashion designers. Her designs have featured in magazines such as Vogue, Marie Claire, Women's Wear Daily  and InStyle and featured on the television series Sex and the City.  Customers include celebrities Liv Tyler, Miley Cyrus,  Lindsay Lohan, Stevie Nicks, Suri Cruise,  Julia Roberts,  and The Pussycat Dolls.   Trelise Cooper Ltd. exports to The United States, United Kingdom, Europe, Asia and Australia, and has been awarded a Trade New Zealand Export Award for creating a successful export business. 
Cooper creates three clothing ranges - Trelise Cooper, Cooper by Trelise and Trelise Cooper Kids. She also produces Trelise Cooper Interiors, a fabric range made in association with textiles house Charles Parsons. Her signature fragrance 'Trelise' was launched late 2009. 
The Trelise Cooper design business began in the early 1980s, with her first boutique opening in 1985.  There are now a number of Trelise Cooper flagship stores in cities throughout New Zealand and Australia, including Auckland, Christchurch, Sydney and Melbourne. Specialist concept areas are found throughout New Zealand retailers including Arthur Barnett in Dunedin.  The Trelise Cooper Kids Auckland flagship store is known for its creative interior, winning the supreme award at the 2007 New Zealand Retail Interior Design Awards. 
Cooper shows her three ranges at New Zealand Fashion Week in shows that are often elaborately staged and marked by the use of celebrities, including Charlotte Dawson, Keisha Castle-Hughes and Petra Bagust. In March 2009 Cooper became the first New Zealand designer to stage a fashion show on board the cruise ship Queen Mary 2. 
Cooper is a philanthropist, generously supporting numerous charities. She is a patron of the Breast Cancer Research Trust  and supports Habitat for Humanity. At 2009's New Zealand Fashion Week Cooper initiated an onsite house build to promote this charity.  She is also an environmental supporter, producing eco bags for supermarket chain Progressive Enterprises.  In 2004, Cooper was made a Member of the New Zealand Order of Merit (MNZM) by the Governor-General on behalf of Her Majesty Queen Elizabeth II for services to the Fashion Industry. 
She is married to Jack Cooper, a well known Australasian textile wholesaler who now volunteers his time to charity Habitat for Humanity.
In December 2005, Cooper had an intellectual property dispute with fellow New Zealand fashion designer Tamsin Cooper,  objecting to Tamsin registering her name as a trademark. In July 2007, Trelise Cooper agreed to drop the suit and let Tamsin Cooper operate under her own name.