King made a slow start to his United career, spending two seasons in the reserves and not making his first team debut until 1922, after which he played intermittently for the following two seasons as cover when first team regulars were injured. It was not until established centre back Jimmy Waugh suffered a serious injury in December 1924 that King was given the opportunity to make regular starts. King became a mainstay of the defence for the next three years and played for United at Wembley when they won the 1925 FA Cup Final.