Gregory Nelson Johnston (born January 14, 1965) is a Canadian former professional ice hockey defenceman.
Johnston was born in Barrie, Ontario. As a youth, he played in the 1977 Quebec International Pee-Wee Hockey Tournament with a minor ice hockey team from Barrie.
Johnston played 187 games in the NHL, most of them for the Boston Bruins, but also a few for the Toronto Maple Leafs. He has also played in the AHL for various teams, and in Europe for various teams in Germany's DEL and Sweden's Elitserien.