Fantenberg made the Canucks roster out of training camp as the team's seventh defenceman, but was unable to draw into the lineup. Fantenberg finally made his season debut on December 1, before scoring his first goal with Vancouver two nights later, in a 5–2 win over the Ottawa Senators. Fantenberg made his debut with Sweden national senior team in October 2012. He was later selected to make his full senior debut in the 2016 IIHF World Championship.