Over a 41-year career, Sinclair saw active service in Korea, Malaysia, Vietnam and in relief operations following Cyclone Tracy, and commanded the naval base . He later rose to high command, serving as Director of Naval Plans and as chief project officer during the establishment of the tri-service Australian Defence Force Academy, and then serving as its first commandant. In 1987 he was appointed Flag Officer Commanding HM Australian Fleet, which was redesignated as Maritime Commander Australia the following year. In 1989 he was appointed as Deputy Chief of the Naval Staff but served only briefly until his retirement later that year.