Hennin was born in Prescot and was a product of the St Helens Combination league, having left hometown club Prescot Cables for Bolton Wanderers in June 1949. He had to wait almost five years for his league debut against Tottenham Hotspur. He went on to make 164 league appearances for the club, with his first of his eight goals arriving against Blackpool in January 1957. The following season saw him help Bolton reach the FA Cup final, where he was selected for the 2–0 win over Manchester United.