The son of General Sir Duncan MacGregor, he was introduced to canoeing in the course of a trip to the United States and Canada in 1858.

MacGregor was a champion marksman but turned to boating when a railroad accident left him unable to hold a rifle steady.

The boat he designed was 'double-ended', (modeled after Indian canoes), but built in Lambeth of lapstrake oak planking, decked in cedar covered with rubberized canvas with an open cockpit in the center. It measured 15 feet long, 28 inches wide, nine inches deep and weighed 80 pounds (36 kg) and was designed y to be used with a double-bladed paddle.He named the boat Rob Roy after the celebrated Scottish outlaw of the same name, to whom he was related.

During the 1860s, he had at least seven similar boats built and he sailed and paddled them in Europe, the Baltic and the Middle East.

In 1866, he published A Thousand Miles in the Rob Roy Canoe, which popularised the design and, more importantly, the concept: "in walking you are bounded by every sea and river, and in a common sailing-boat you are bounded by every shallow and shore; whereas, ...a canoe [can] be paddled or sailed, or hauled, or carried over land or water".

The book was internationally successful; with subsequent books and public appearances, it earned MacGregor more than ten thousand pounds. Scottish author Robert Louis Stevenson's 1876 voyage by canoe through the canals and rivers of France and Belgium, published in 1878 as An Inland Voyage, used "Rob Roy" canoes.

Died 1892 in Bournemouth.