Sir Adetokunbo was called to the bar at the Middle Temple in London in 1934. After returning to Nigeria and at the insistence of his father, he joined the Civil Service and from 1934–35, he worked as crown counsel in the Office of the Attorney-General. He then joined the unified Nigerian administrative service and for a year, he was posted to Enugu as assistant secretary at the southern secretariat, Eastern Nigeria. He left the service and started a private practice from 1936 until 1939, when he was appointed Magistrate of the Protectorate Court. In 1938, he joined the Nigerian Youth Movement. As a magistrate, he was posted to various Nigerian towns; Ademola worked in Warri from 1939-1946, and then returned to Lagos in 1946 to preside at St Anna Court. In 1947, he was posted to Opobo. In 1949, he became the third Nigerian to be appointed a puisne judge. In 1948 he served as a member of the commission for the revision of court legislation.
