He captained the team to the Southern Division Championship before committing to play collegiate hockey with the Colgate Raiders of the ECAC conference in the NCAA.

Wagner's development promise gained notice and as a result was he was selected by the Anaheim Ducks in the 2010 NHL Entry Draft.

[3] Wagner made his professional debut with the Ducks' AHL affiliate, the Norfolk Admirals to open the 2012–13 season, in a contest against the Worcester Sharks on October 12, 2012.

Approaching the final year of his entry-level deal, Wagner was amongst the last cuts to make the Ducks opening night roster for the 2014–15 season.

At the conclusion of the Admirals season he was recalled for the Ducks post-season and made his playoff debut in the opening round victory over the Winnipeg Jets.

[10] As the Ducks extra forward, he featured in one game before he was exposed to his waiver eligibility, upon being assigned to new AHL affiliate, the San Diego Gulls on October 21, 2015.

[citation needed] On July 1, 2018, having left the Islanders as a free agent, Wagner signed a two-year deal worth $2.5 million with his hometown club the Boston Bruins.

[23] Following five seasons within the Bruins organization, Wagner left as a free agent and was signed to a one-year, two-way contract in a returning to former club, the Colorado Avalanche, on July 1, 2023.

[25] He missed the first half of the season rehabilitating his injury before he was placed on waivers and re-assigned to AHL affiliate, the Colorado Eagles, upon his return to health on January 11, 2024.