His watercolours of local events and scenes were reproduced as monochrome wood engravings so they could be included in these weekly periodicals.
[5] In 1870, Armstrong accompanied the Wolseley Expedition to the Red River Colony, recording the incredible effort required to move the military force through the Canadian wilderness.
He exhibited with the Ontario Society of Artists[7] and was a member of the Royal Canadian Academy of Arts until 1887, when he resigned.
He painted the watercolour The Arrival of the Prince of Wales at Toronto (1860) which hangs in the National Gallery of Canada in Ottawa, Ontario.
His watercolour painting, Thunder Cape, Lake Superior (1867), hangs in the National Archives of Canada.