The Winger was in irresistible form for Brendan Rodgers' side as he guided his team to their first away win of the Scottish Premiership season.
He scored goals in the 15th, 30th, 38th and 45th minutes in a remarkable performance. Forrest had not yet scored in six appearances this season but changed that in spectacular style.
He became the first Celtic player to score four goals away from home since Marciej Zurawski, who achieved the feat in 2006 against Dunfermline.
Odsonne Edouard scored Celtic's second goal, while Callum McGregor added the sixth late on after Danny Swanson was sent off for the home team at the beginning of the second half.