Henry married Mary Castleton Osborne on 28 April 1915 and began working for another engineering and patents company owned by S. Oldfield and D. B. Hutton.

Henry struck a hard bargain in purchasing the New Zealand Perpetual Forests assets and was made the chairman and managing director of the new company for his efforts.

He travelled extensively throughout the United States and Europe to find the newest processing technology and fought a protracted battle with the New Zealand government to overcome bureaucracy.

In the 1954 Queen's Birthday Honours, Henry was appointed a Knight Bachelor in recognition of his role as chairman and managing director of New Zealand Forest Products.

However, he showed no interest in retiring as chairman of New Zealand Forest Products, and continued to battle the government over industry licensing, while beginning to display increasingly erratic behaviour.

In his history of New Zealand Forest Products, titled A Hundred Million Trees, Brian Healy said "Sir David Henry lacked warmth and humour in his working relations and tended to be abrupt and demanding with his subordinates.

Yet he was a fluent and persuasive speaker whose self-assurance, business acumen and tenacity were vital in enabling New Zealand Forest Products to overcome enormous barriers and to develop into one of the country's largest industrial enterprises."