Self-published author Finn Bell won the award for best first novel for his thriller Dead Lemons.
The awards, presented in Christchurch on Saturday, recognise excellence in crime fiction, mystery and thriller writing.
Mr Bell was also a finalist in the best crime novel category for Pancake Money, becoming the first author to be nominated in two categories in the same year.
With a background in forensic psychology, Mr Bell took inspiration for the stories from his experience working in prisons, hospitals, night shelters and for charities.
''I started just keeping a diary and journalling to help me deal with stuff that I brought home from work.''
The diaries evolved into a ''big, confusing, very insane'' book.
His partner, Lisa Miers, suggested separating the stories into two books.
Both novels were written at the same time and had shared characters.
''I'm just starting out my writing career so I did not expect at all that I would be in the running [for a Ngaio Marsh Award].''
His books were also available only in electronic format, which was unique for the win.
Winning the best first novel category came as a ''complete shock and surprise''.
''I did make a speech. I can't remember what I said.''
When he first published the books last year, he did not think he would be nominated for or win an award.
''Definitely not. If I was going to win an award, the Ngaio Marsh of all things.''
The judges called him a ''wonderful new voice in crime writing'' who delivered a tense, compelling tale centred on an original, genuine and vulnerable character.
Dead Lemons explores themes of ''addiction, loss and recovery'' as a wheelchair-bound man escapes to a remote cottage in Southland.
All of Mr Bell's books were based in the South Island.
Film-maker Michael Bennett, of Te Arawa, won the inaugural best non-fiction category for In Dark Places.
Fiona Sussman won best crime novel for The Last Time We Spoke.
She is the first woman to win the award since it started in 2010.
The awards were announced at the Great Literary Quiz and Ngaio Marsh Awards event in Christchurch on Saturday.
