A tough, physically strong centre-back, Niccolai initially began his career with Torres in 1963, before joining Cagliari Calcio, where he played from 1964 to 1976, winning the only Serie A championship in the club's entire club history in 1970. He ended his career in 1977 with Perugia. Niccolai played 218 Serie A matches, and is still remembered today for his proneness to score own goals, including some very spectacular ones.