Conacher's first full season with the Senators was a difficult one, as he struggled to find offensive consistency. Through his first 58 games of the season he recorded only four goals and was a healthy scratch on multiple occasions. Conacher's offensive struggles were perhaps magnified by the fact that goaltender Bishop, the player he had been traded for, was playing very well in Tampa Bay and was frequently receiving mention as a Vezina Trophy candidate. On March 4, 2014, the eve of the 2013–14 NHL trade deadline, Conacher was placed on waivers by the Senators. He was subsequently claimed by the Buffalo Sabres on March 5, 2014.
The Sabres declined to offer Conacher a contract extension, which allowed him to become a free agent on June 30, 2014. The team was undecided in regard to retaining his rights, only deciding at the last minute to release him.
On July 1, 2014, Conacher was signed as a free agent by the New York Islanders on a one-year, $600,000 contract. After playing in 15 of the team's first 29 games, Conacher was placed on waivers by the Islanders on December 12, 2014. He cleared waivers and was assigned to the team's minor league affiliate, Bridgeport Sound Tigers, the following day. On March 2, 2015, Conacher was traded to the Vancouver Canucks, in exchange for Utica Comets player Dustin Jeffrey. He was assigned to AHL affiliate, the Utica Comets, securing an offensive role to help the club reach the Calder Cup finals.