In June 1958, Mitten left Mansfield and joined Newcastle United. Initially, he enjoyed success at the club and steered the club to a pair of solid mid-table finishes, despite an ongoing power struggle between chairman William McKeag (who had installed Mitten and gave him full control over the team) and director and former manager Stan Seymour (who felt the board should be able to veto Mitten's tactics and team selections). Newcastle gained a reputation for free-scoring football under Mitten, but they also proved to be defensively frail, and they ultimately paid the price for this in 1961, when they were relegated after a season in which they scored 86 goals but conceded 109. Mitten was allowed to remain in charge and attempt to steer the club back into the First Division, but instead they found themselves fighting relegation to the Third Division, eventually resulting in Mitten's dismissal a few months into the season. While at Newcastle, he was also involved in the George Eastham affair, which involved another player who challenged the authorities on player's rights.