Royall was born on July 24, 1894, in Goldsboro, North Carolina, the son of Clara Howard Jones and George Pender Royall. He graduated from the University of North Carolina at Chapel Hill, where he was a member of the Delta Kappa Epsilon fraternity, and Harvard Law School before serving in World War I. He then practiced law and was elected to the North Carolina Senate as a Democrat. At the beginning of World War II, he became a colonel in the US Army. On August 18, 1917, Royall was married to the former Margaret Pierce Best, with whom he had two sons and one daughter, Kenneth Claiborne, Jr., Margaret, and George Pender Royall. According to a 2006 newspaper column by Jack Betts, eight Nazisbent on mayhem came ashore on Long Island in 1942 but were soon caught and ordered to stand trial in a secret military tribunal. US President Franklin Roosevelt appointed Royall to defend them, but Roosevelt wanted no foolishness. He wanted the Nazis executed as soon as possible. Royall's orders were to stay away from civilian courts. Royall wrote to Roosevelt that he thought that the president had no authority to convene a secret court to try his clients, and Royall asked Roosevelt to change his order. The president refused, and Royall appealed to the US District Court and argued that the secret tribunal was unconstitutional. The court rejected that argument and so Royall and other lawyers in his office appealed to the Supreme Court. The Supreme Court rejected Royall's argument in a brief announcement in July 1942 and upheld the right of the president to appoint a secret tribunal. However, Royall had succeeded in getting civilian court review of the tribunals' constitutionality despite the president's preference to hush things up. The Supreme Court published a more detailed opinion in October, saying, "Constitutional safeguards for the protection of all who are charged with offense are not to be disregarded." By then, six of Royall's clients were dead. They were tried, convicted, and executed in August 1942, only days after the Supreme Court's brief announcement upholding Roosevelt's tribunals. Two were sent to prison. Royall later said he believed his defense of the Nazis was his most important work in a long and illustrious career. He was promoted to brigadier general.
Royall served as Undersecretary of War from November 9, 1945 until July 18, 1947. President Truman named him Secretary of War in 1947. He became the first Secretary of the Army two months later. Royall was forced into retirement in April 1949 for continuing to refuse to desegregate the Army, nearly a year after President Truman promulgated Executive Order 9981.
In December 1949, Royall became a partner at the prestigious New York Citylaw firm of Dwight, Harris, Koegel and Caskey, becoming the firm's head in 1958. The firm was later renamed Rogers & Wells, and it was subsequently known as Clifford Chance Rogers & Wells after its merger with British firm Clifford Chance. Royall died in Durham, North Carolina, on May 25, 1971, aged 76. He was buried at Willow Dale Cemetery in Goldsboro, North Carolina. His son, Kenneth C. Royall, Jr. served in the North Carolina House of Representatives from 1967 to 1972, and the state Senate from 1973 to 1992.
