Charles Oppenheimer was born in Chorlton-upon-Medlock, Manchester, on 10 October 1875. His father was from a German Jewish family in Brunswick, and his mother was from Montrose, Scotland. Charles was a prize-winning student at Manchester School of Art, and his first picture was exhibited at the Manchester Academy of Fine Arts in 1894, though the title of the work is now lost. His studies also took him to Italy in 1868, and he returned there in 1898 and again 1912.

Oppenheimer married Constance Emily Taylor in 1903, and in 1908 - after a chance meeting with Ernest Archibald Taylor (1874-1951), the Scottish designer and painter - the couple moved to Kirkcudbright in Scotland, first to a home rented from Edward Atkinson Hornel (1864-1933), another of his associates. In Kirkcudbright, the light suited Oppenheimer as it did the other artists working there. By this time Oppenheimer too had established himself, having exhibited his first picture at the Royal Academy in 1906, Old Mills, Montreuil, and having a line drawing published in the Manchester Guardian, 1906. He had also exhibited A Whitby View, a watercolour, and The end of the day, an oil, in Liverpool.

During the First World War, he served with the Royal Garrison Artillery and his unit was the 180 Siege battery. He saw action around Bethune and Lens. He was also engaged with the 1 Corps Intelligence Section. A year after the Armistice, Oppenheimer donated his watercolour The Green Crassier, Lens to the Imperial War Museum.

Other works over six decades include: The Lion of St. Mark, Venice, exhibited 1898, illuminated manuscript The Eve of St. Agnes (c. 1901), Kirkcudbright Harbour (c. 1910), Kirkcudbright (c. 1913), Verona (1914), Morning mist - Lake of Lugano (c. 1925), Siena at dusk (c. 1929), San Francesco, Assisi (1930s), and Blossom, Buckland Burn (c. 1940). Oppenheimer exhibited at the Royal Academy in London, the Royal Scottish Academy, at the Royal Scottish Academy of Painters in Watercolours (RSW), at the Royal Glasgow Institute of Fine Arts, the Aberdeen Artists' Society, and in Liverpool. He designed a number of posters for Britain's railways, depicting local beauty spots, and he also designed the badge and motto 'Sempere Vigilo' of the Scottish Police Force (now Police Scotland).

Oppenheimer helped to found the Dumfries and Galloway Fine Art Society, and he was a special constable in Kirkcudbright and also served on Kirkcudbright Town Council.

Charles Oppenheimer died in Kirkcudbright on 16 April 1961.