After serving his apprenticeship with a druggist in his native town, Swan became first assistant and later partner in a firm of manufacturing chemists in Newcastle. Working with wet photographic plates, he noticed that heat increased the sensitivity of the silver bromide emulsion. By 1871 he had devised a method of drying the wet plates, initiating the age of convenience in photography. Eight years later he patented bromide paper, the paper commonly used in modern photographic prints.

Some years earlier, in 1860, Swan developed a primitive electric light, one that utilized a filament of carbonized paper in an evacuated glass bulb. Lack of a good vacuum and an adequate electric source, however, resulted in a short lifetime for the bulb and inefficient light. His design was substantially the one used by Thomas A. Edison nearly 20 years later. In 1880, after the improvement of vacuum techniques, both Swan and Edison produced a practical light bulb. Three years later, while searching for a better carbon filament for his light bulb, Swan patented a process for squeezing nitrocellulose through holes to form fibres. In 1885 he exhibited his equipment and some articles made from the artificial fibres. The textile industry has utilized his process. Swan was knighted in 1904.