Tennant was born in Russell Square, London, the second daughter of Charles Tennant and Gertrude Barbara Rich Collier (1819–1918). Her sister was the photographer, Eveleen Tennant Myers. She studied painting under Edward Poynter at the Slade School of Fine Art, London and with Jean-Jacques Henner in Paris. She first exhibited at the Royal Academy in 1886 and subsequently at the New Gallery and the Grosvenor Gallery in London. Outside of London Tennant featured in exhibitions by the Fine Art Society in Glasgow and also in the Autumn Exhibitions held in Liverpool and Manchester.
In 1890, she married the explorer of Africa, Henry Morton Stanley, and became known as Lady Stanley. She edited her husband's autobiography, reportedly removing any references to other women in Stanley's life. Stanley had an unusual life and had been involved with young boys too.
Lord Henry Morton Stanley (1841–1904) (1880)