Wilhelm August Rudolf Lehmann (19 August 1819, Ottensen near Hamburg – 27 October 1905 Bushey) was a German-English portraitist and author.

Lehmann was born near Hamburg the son of painter Leo Lehmann. He and his elder brother Henri Lehmann studied in Paris at the École des Beaux-arts, in Rome, and with the painters Peter von Cornelius and Wilhelm von Kaulbach. Lehmann's major painting, The Blessing of the Pontine Marshes by Sixtus V was shown in Paris in 1846 and bought by the French government.

In 1866 Lehmann settled in London, became a British citizen, and painted his best known portraits. He married Amelia Chambers, daughter of the Scot author and naturalist Robert Chambers. Amelia's sister Nina married Lehmann's younger brother Frederick, and the extended social circle of the two couples included Charles Dickens, George Eliot, Robert Browning, Lord Leighton, and other prominent figures.

In 1896 a number of his engraved portraits were collected and published as Men and Women of the Century.

One of Lehmann's daughters was Liza Lehmann, who became a notable English soprano and composer. Lehmann was the uncle of the British journalist and politician Rudolf Chambers Lehmann.