His father had been a captain in the Royal Navy, serving during the American Revolutionary War, and then was the harbour master of Montreal.

[2] Around 1824, Armstrong moved with his parents to Berthier, where he established himself as a merchant, as well as an agent for insurance companies.

She was the daughter of Jacques Deligny, who had been a member in the Legislative Assembly of Lower Canada for over twenty years, first for the district of Warwick, and then for Berthier.

[1] His daughter Amélie married Michel Mathieu, who served in the Canadian House of Commons.

Following Sydenham's death in late 1841, he continued to oppose the government of the new Governor General, Sir Charles Bagot, until Bagot was forced to reorganise his government by taking in Reformers, led by Louis-Hippolyte Lafontaine and Robert Baldwin.

Armstrong supported the new government, and also voted in opposition when the Lafontaine–Baldwin ministry felt compelled to resign.