Greaves later served as Chief of Minority Staff for the 1945–1946 "Joint Congressional Investigation of the Pearl Harbor Attack".
Greaves was a longtime associate and friend of Ludwig von Mises, regularly attending his seminars.
"[5] Greaves was nominated as the 1980 presidential candidate for the American Party, with Frank L. Varnum as his running mate.
[6] The state parties of Kansas and Minnesota were unhappy with Greaves's moderate stance on abortion and put anti-Greaves tickets on their ballot lines, winning 1,555 and 6,136 votes respectively.
In 2010, Percy's wife completed an unfinished manuscript left behind after his death and it was published posthumously by the Ludwig von Mises Institute as Pearl Harbor: The Seeds and Fruits of Infamy.