After pushing crayon to its limit as a medium—although he was never to abandon it entirely—Cotes turned to oil painting as a means of developing his style in larger-scale works.

After 1746, the costumes in his pictures were mostly executed by the specialist drapery painter Peter Toms.

[2] One of the most fashionable portrait painters of his day, Cotes helped found the Society of Artists of Great Britain and became its director in 1765.

At the peak of his powers, Cotes was invited to become one of the first members of the Royal Academy, but died just two years later, aged 44, in Richmond.

He also taught pastel skills to John Russell, who described Cotes' techniques in his book The Elements of Painting with Crayon.