Alexander was the director of the Newcastle firm M. Alexander and Sons, who were active in the field of cinema design throughout the 1920s and 1930s, producing some hundreds of schemes for cinema interiors, mostly in the North East. Much of this work was for the Empire chain, but they also designed for the Essoldo and Regal circuits. The Black's Regals at Byker and Gateshead were examples. Alexander's work anticipated the Art Deco effects which became the hallmark of the Odeon cinemas up and down the country.
Few of Alexander's cinemas in the North East are left standing and none of his exquisite romantic interiors survive, though until a few years ago there were buildings which could be identified: the Apollo and Olympia in Birtley, the Olympia at Blackhill and Consett, the Low Fell Capitol, the Moderne at Norton-on-tees, the Electric at Prudhoe, both Victoria and Albert cinemas in Stanley, as well as others in Stockton and Middlesbrough.

John Alexander was also responsible for interiors elsewhere, notably the Green Playhouses in Glasgow and Dundee, and, in 1936, the Northwick cinema in Worcester, fortunately still intact. Though painted in the wrong colour, it preserves the superb mythical figures, horses and chariots flanking the proscenium arch, designed and manufactured by Alexander at a cost of £1138. This precious survival makes us regret even more the fabulous North East interiors which have gone.
Up until his retirement in 1954, John Alexander, assisted by a team of talented women artists, went on producing coloured perspective drawings, often in browns, greens and violets, as much for his own pleasure and satisfaction as for showing clients the pastel elegance of the dream-palace they would be getting. As David Atwell writes in his Cathedrals of the Movies: 'What his drawings represent is a unique record of the period and the enthusiasm that went into cinema decoration. Perhaps more than any photograph can ever achieve, these perspectives convey the atmosphere of the heyday of the super-cinemas of the 1930s, a field where so little survives now after progressive modernisation, conversion and redevelopment.'