Mercer was active as a photojournalist in New Zealand from 1980 to 1986, during which time he became involved in and photographed a number of activist events.

Mercer photographed the ensuing action of protestors, police, rugby fans, and bystanders.

Before moving to Adelaide at the end of 1985, he left a selection of photographic prints with the Waikato Art Museum.

[1] A collection of Mercer's work from this time is also held by Auckland War Memorial Museum, including photographs of the third test at Eden Park on September 12, 1981.

[5] With his partner, Deborah Taylor, he also founded Cameraworks, a business offering custom commercial photography and a black-and-white film processing and printing service.