Barney Barnato (4 July, 1852 - 4 July, 1897), born Barnett Isaacs Barnato, was a South African diamond magnate.

Born in a slum in Whitechapel, London, he joined his brother Harry in Cape Colony in 1873 during the "diamond rush" which accompanied the discovery of diamonds at Kimberley. His brother had gone out in 1871 and had been working as a comedian and conjurer, and his younger brother wanted to join in, calling out, "And Barnett, too!!". The oft repeated phrase evolved, to the point which Issacs changed his name to Barney Barnato.

He formed the Barnato Diamond Mining Company and within ten years he had become a millionaire, primarily by buying worked-out diamond mines area and mining the abandoned blue earth heaps.

He competed with Cecil Rhodes in taking over the diamond mining industry in Cape Colony by aggressive buying out of competitors, although in the end Rhodes succeeded in buying him and his brother out for around four million pounds, writing the single largest check in history at that point. Barnato subsequently became Kimberley's member of parliament in the Cape Parliament from 1889 until his death.

He reportedly committed suicide by jumping into the ocean and drowning from a ship taking him to England in 1897. However, his family vigorously rejected that theory, as it was so completely against the character of a man who had been a pioneer in the rough and ready days of emerging Southern Africa. His body was recovered and buried in Willesden cemetery, near London.