Armstrong was born in what would soon become the province of Ontario in 1867. After briefly teaching school, he entered the business industry, as a druggist. After initially gaining experience in politics on the council of Eastnor Township, he relocated west to the city of Edmonton, Alberta. In Edmonton, he established his pharmaceutical business once again and worked briefly with his brother on real estate and construction projects. In 1907, he ran for election to the Edmonton City Council and was elected to a two-year term. In 1910, he decided to run for the mayoralty in the municipal election; uncontested as the only nominated candidate on election day, Armstrong was acclaimed to the mayor's chair for the upcoming year. During his term, several issues were brought up to attention, including the city's need of a new civic building and the possibility of two new gas plants for the city.