Born at Gallen Priory in County Offaly, Armstrong was the son of Edmund Armstrong and his wife Elizabeth, third daughter of Frederick Trench and sister of Frederick Trench, 1st Baron Ashtown.
[2] He became Receiver General of Stamps in Ireland in 1831, an office he held until its abolition in 1841,[4] when he was created a baronet, of Gallen Priory, in King's County as compensation.
[5] In February of the same year, he entered the British House of Commons in a by-election, sitting for King's County until 1852.
[4] His youngest son, Charles Nesbitt Frederick Armstrong (1858–1948), born when his father was 71 or 72, went to Queensland, Australia, and married Helen Porter Mitchell (the opera singer, Dame Nellie Melba) in 1882.
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