The future Lord Armstrong was born in Newcastle, at 9 Pleasant Row, Shieldfield. He was articled to Armorer Donkin's firm of solicitors in the town but his heart lay elsewhere and he soon moved into engineering. The first hydraulic crane, the foundation of his great enterprise at Elswick, was erected on Newcastle Quayside in 1846 and attracted wide attention. To cope with locations which lacked a sufficient head of water, Armstrong devised the accumulator tower, a splendid example of which dominates Grimsby docks.
Armstrongs produced hydraulic machinery, cranes and bridges, soon to be followed by artillery, notably the Armstrong breech-loading gun, which re-equipped the British army after the Crimean War. The guns were tested above Allendale. Amusingly enough, when in the area of Alston Moor, Armstrong would attach the letters MD after his name. This signified 'Maister of the Drallikers' , a name given to him by an Allendale miner who saw him putting in the hydraulic engines in the dale.

The Armstrong gun was also supplied to the Union side in the American Civil War. Rifled and throwing a shell-shaped projectile, the Armstrong gun is regarded as marking the birth of modern artillery. Armstrong handed over the rights of his gun to the nation, and received a knighthood. The 12-pounder rifled breech-loader (R.B.L.) was introduced in 1881 and its great superiority over any previous gun was convincingly demonstrated. As a result, it was adopted as the equipment for both horse and field artillery. Such was Armstrong's fame that he is thought to be a possible model for Bernard Shaw's arms magnate in Major Barbara.

The famous hydraulically-powered Swing Bridge on the Tyne dates from 1876 and Armstrongs provided the lifting gear for Tower Bridge in 1894. Shipbuilding began in 1882 and Armstrongs built great numbers of vessels for the world's fleets, including warships, complete with armament, for the emerging Japanese navy. Armstrong's was not afraid to pay for the best, and gathered many excellent engineers at Elswick. Notable among them were Andrew Noble (q.v.) and G.W. Rendel (1833-1902)., who came to live with Armstrong when he left school, in order to study engineering. He became a partner in the Elswick concern in 1858 and, in conjunction with Noble, directed the ordnance works, himself specialising in naval gunnery and warships. His design of gun-mountings and hydraulic control of gun-turrets were adopted world-wide. Rendel introduced the cruiser as a naval vessel.

In 1906, a four-gun battery, armed with the new Armstrong 60-pounder, was allotted to each infantry division of the British Army, with ammunition consisting of 70% shrapnel and 30% high explosive. In 1914, on the western front, the 60-pounder was described as a really excellent gun. It had a range of 10,500 yards which was later increased to 12,300 yards. Towards the end of World War I, a mark II design was produced with a range of 16,000 yards. The 'backbone of the British artillery effort' was the 18-pounder produced in the main by Armstrongs, along with Vickers. Lloyd George had chosen a small group of trustworthy armaments firms to cope with the demands of the war and Armstrong Whitworth was among them.

Lord Armstrong's impressive monument stands at Barras Bridge in Newcastle, near the university. He donated Jesmond Dene to the city, as well as Armstrong bridge and Armstrong Park nearby. He lived in the house which is now the Fisherman's Lodge restaurant. Armstrong's great mansion 'Cragside' near Rothbury, built by Norman Shaw, is of romantic Wagnerian splendour. The house was the first in the world to be lit using hydro-electricity and visitors today can see the ingenious devices by which power is supplied from reservoirs high on the hillside - a thousand acres planted with magnificent trees and rhododendrons. The tallest tree in England is among the Douglas firs in front of the house. Here Armstrong entertained visitors from all over the world, including the Shah of Persia and the son of the Emperor of Japan. Lord Armstrong died at Cragside and lies in Rothbury churchyard.