Fábio Vieira’s penalty was all Arsenal needed to seal the Community Shield at Wembley Stadium, London.
Manchester City had thought a stunning strike from Cole Palmer would be enough, but a stoppage-time leveller took the match to penalties at Wembley.
Trossard scored in the 101st minute level it up right at the end of stoppage time to equalise fort he Londoners.
The victory is the 17th time in the club’s history they will lift the trophy.