Born in 1810 at Newcastle-upon-Tyne, Armstrong was originally launched on a career in law. However, his major interest was in engineering. In 1840, he invented a hydraulic engine, following it up with other electrical and labour-saving devices, including the hydraulic crane. In 1847, he founded the Elswick works at Newcastle, to produce various electrical devices and engines. The Armstrong breech-loading gun was one of his more successful developments, and in 1882 the works also began building ships. In 1897, the firm merged with Joseph Whitworth & Co, later becoming Vickers Armstrong Ltd.
Lord Armstrong purchased Bamburgh Castle as one of his residences, and also built the Victorian extravaganza, Cragside (now a National Trust property), further inland. The latter was the first house in Britain to be entirely powered by hydro-electricity, generated by a system of Armstrong's own design. Armstrong himself died in 1900.