Sir William Boxall RA (29 June 1800 – 6 December 1879) was an English painter and museum director.

Initially hoping to make his name as a history painter, Boxall later had to turn to the more lucrative genre of portraiture.

Among his friends were William Wordsworth, whose portrait he painted, the sculptor John Gibson and the painter Sir Edwin Landseer.

His directorship lasted eight years, during which he oversaw the construction of Edward Middleton Barry's celebrated eastern extension.

The authenticity of the former was called into question by the House of Lords in 1869, but is now generally regarded to be genuine – unlike another of Boxall's controversial acquisitions, the "Suermondt Rembrandt" 7, now attributed to Nicolaes Maes.