Viktor Kassai is a Hungarian football referee. He has been a full international referee for FIFA since 2003.

Kassai was the head of an all-Hungarian crew in the 2011 UEFA Champions League Final at Wembley Stadium in London, where he cautioned two players apiece on both the Barcelona and Manchester sides. He also refereed in 2012-13 UEFA Champions League.

Kassai refereed in UEFA Euro 2008 as the fourth official in several matches. During 2008, he also officiated in the 2008 Olympic Games, including in the final. Kassai was preselected as a referee for the 2010 FIFA World Cup. He refereed in the first leg of the AFC 5th vs OFC winner qualifier between Bahrain and New Zealand. On 5 July, it was announced that he would be in charge for the Germany vs Spain semifinal. It was his 4th match in the World Cup. This is the highest prestige match a Hungarian referee has been in charge of since Sandor Puhl's 1994 FIFA World Cup Final. He also refereed in UEFA Euro 2012. In December 2015, he was named one of the eighteen referees appointed for UEFA Euro 2016.