Although born in Auckland, Cowan spent his childhood in Kihikihi, on the border of the King Country,The farm was on land confiscated from Waikato Maori, and contained part of the site of the battlefield of Orakau. Settler militia were based at a military blockhouse close to his home, while there was a considerable Maori community in the area, and the young Cowan grew up speaking both English and Maori. He never lost his fascination with Maori culture and the Land Wars.

From 1887 to 1902, James Cowan was employed as a journalist for the New Zealand Herald in Auckland. His first books were published in 1901, a guide to Taupo and a catalogue of the Maori paintings of Gottfried Lindauer. In 1903, he began work for the Department of Tourist and Health Resorts in Wellington, writing magazine articles and books to promote tourism. ' New Zealand, or, Ao-teä-roa (the long bright world): its wealth and resources, scenery, travel routes, spas, and sport' was written during this period.

By 1909, Cowan was a freelance writer. The Maoris of New Zealand, written in 1910 was a general survey of Maori and in 1911, he wrote The adventures of Kimble Bent an American who deserted the colonial forces during the land wars and who lived alongside their Maori foes.

From 1918 until 1922, Cowan was paid by the Department of Internal Affairs and worked on The New Zealand wars: a history of the Maori campaigns and the pioneering period. Other books on colonial topics included The old frontier: Te Awamutu, the story of the Waipa Valley in 1922, Tales of the Maori coast in 1930, Tales of the Maori bush in 1934 and Hero stories of New Zealand in 1935. Cowan also wrote on Maori ethnography for the Journal of the Polynesian Society and The Maori yesterday and to-day, and co-wrote Legends of the Maori with Maui Pomare.

The First Labour Government granted James Cowan a pension in 1935, one of the first two New Zealand writers to receive state support. The deputation asking for this support said of Cowan he 'had never made any money out of his historical books but had done very good work for the country'