Born in Auckland and raised on the city’s North Shore, Duggan was mentored by Frank Sargeson and was friendly with many of the important writers of the day, including Greville Texidor, John Reece Cole, Keith Sinclair and Kendrick Smithyman.
Duggan displayed no interest in literature as a child, but the loss of his left leg in 1940 through acute osteomyelitis generated his desire to write.
In 1960 Duggan was the second recipient of the newly established Robert Burns Fellowship (the first was Ian Cross), which provided a writer with a lecturer's salary for one year at Otago University.
His story 'Six Place Names and a Girl,' to which Sargeson contributed the title, was an early success, with its minimal plot and its brief, evocative descriptions of the Hauraki Plains.
In the early 1960s Duggan published two stories in Landfall, ‘Riley’s Handbook’ and ‘Along Rideout Road that Summer,’ which moved New Zealand literature decisively away from its long-dominant tradition of social realism.