In the late 1930s Moynihan was associated with the Euston Road School, committed to realist painting. In 1940 he trained as an artillery man and was commissioned in camouflage before becoming a war artist in 1943. Many of his portraits of high-ranking officers and advisers are now in the Imperial War Museum. His portraits were often swiftly executed but sensitively observed. Influenced by artists such as Edouard Manet and Diego Velazquez, Moynihan used a rich sensuous brushstroke to convey a sense of this young service woman's physicality. During the war women were urged to look their best at all times to boost morale. Lipstick became known as the 'red badge of courage'.