David Allan Poe Watt was born on April 2, 1830, in Ayrshire, Scotland.

He was a merchant, lobbyist, social reformer, and amateur naturalist. He was educated in grammar schools in Scotland before arriving in Montreal in 1846. Watt entered the mercantile trade as a commission merchant and broker specializing in produce. He served as treasurer of the Montreal Board of Trade from 1862 to 1865. He worked tirelessly throughout his career to protect and promote the commercial interests of Montreal merchants. Watt was also one of the organizers of the Montreal Corn Exchange, the Citizens' League, and the Montreal Art Association. Around 1882 he went into business for himself as a broker, and later he became a grain merchant. In 1912, he accepted the post of manager of North American export freight for Hugh Allan’s Montreal Ocean Steamship Company (the Allan Line), a post he held until his death. Watt contributed articles on North American ferns to the Canadian Naturalist and served as its editor.

In 1857, he married Frances Macintosh (1826–1876)). He died on December 13, 1917, in Montreal, Quebec.