Industrialist and politician. Educated at Ayr Academy and in Tillicoultry, he was the grandson of industrial chemist Charles Tennant (1768 - 1838) and inherited his business, the immense St. Rollox Chemical Works, which produced alkalis and bleaching powder, used extensively in the textile industry. He greatly expanded the business, building new plants and extending it into copper, iron, steel and gold, with mines in Spain, South African and India. He worked with the Swedish explosive pioneer Alfred Nobel to found Nobel's Explosives Co Ltd. in Glasgow in 1877. Tennant was also Chairman of the Union Bank of Scotland and a Director of the North British Railway. He eventually brought together more than 45 separate companies to form the United Alkali Company in 1890 which, with Nobel interests and others, combined to form the chemical giant Imperial Chemical Industries in 1926.
Tennant served as Liberal Member of Parliament for Glasgow (1877-80) and for Peebles and Selkirk (1880-86). He bought The Glen in Peeblesshire in 1853 and remodelled Glen House, where he lived the life of a country gentleman, dispensing generous hospitality. He was also noted for lavish parties at his London home in Grosvenor Square.
Tennant died in Surrey and was buried in Traquair churchyard, leaving a multi-million pound fortune.