"I knew as soon as I saw it that he was someone who had already been extremely active. I could see immediately that Wanganui had a very special artist in its midst," Mr Milbank said.
During 40 years of painting Mawhinney moved from figures and faces to architecture. He often painted in egg tempera, a mixture of egg yolk and water colour.
Whatever the subject, his paintings were always spare and controlled. At first they were pretty but became more challenging and often had a sense of mystery and foreboding.
Mawhinney was a very private person, who read and travelled widely. Painting was his only hobby, and he threw himself into it.
After initial reluctance he went on to exhibit in Hawke's Bay and Wellington as well as Wanganui.
During the last year of his life he was especially prolific and Mr Milbank said his work took off in a new direction.
It is now scattered widely, and collected by several people.
After Monday there will still be a few Mawhinney works at the WHMilbank Gallery for its next exhibition, Their Work Lives On: Neville Mawhinney 1928-2010 & Don Driver 1930-2011. That show is to finish on May 12.