On October 18, 2011, Voynov made his NHL debut with the Kings in a 5–0 win against the St. Louis Blues. On October 27, 2011, He scored his first NHL goal against Kari Lehtonen of the Dallas Stars in a 5–3 win. He also scored another goal in that game. On June 11, 2012, Voynov was able to win the Stanley Cup with the Kings. During the 2012–2013 playoffs, he set a Kings record for number of goals scored by a defender during playoffs. He scored a fifth playoff goal during the third game of the semifinals.