[1] Armstrong owned a pastoral property called Adare, which was one of the Lockyer Valley's largest cattle properties of the 19th and 20th centuries, and had its homestead approximately seven kilometres north of Gatton on Adare Road.

Armstrong moved the original homestead from a site on the edge of Lake Clarendon in 1896.

He was Chairman of Committees from 1910 to 1911 and Speaker of the Legislative Assembly from 1911 until the conservative government's defeat by T. J. Ryan in 1915.

[4][5] He was described as "a typical country squire, perhaps the last of the squirearchy that had come down from earlier parliaments", with the Assembly under his speakership described as "stiff and formal".

His nephew (son of his sister) William Vanneck, 5th Baron Huntingfield was Governor of Victoria from 1934 to 1939.