Kovar had 162 points (60 goals, 102 assists) in 236 games with Plzen HC in the Czech Extraliga, the top league in the Czech Republic, from 2008-13. He has played for the Czech Republic in five IIHF World Championship tournaments (2013-17).
The Islanders also agreed to terms with forward Ross Johnston on a four-year contract. Johnston, 27, had six points (three goals, three assists) in 24 games with the Islanders and 11 points (three goals, eight assists) for Bridgeport of the American Hockey League last season.