After one season at the Rochester Institute of Technology, decision time arrived for Tanev. The undrafted defenseman wanted to join an NHL organization, and there were several teams interested.

Foregoing his final three years of college eligibility, the Toronto-born Tanev signed a free agent contract with the Vancouver Canucks on May 31, 2010.

Considered too small to play midget hockey (5 feet, 120 pounds), Tanev instead played with his high school team in the 10th grade and thought about quitting the game. Two years later, after a growth spurt, he enrolled to play at RIT.

There, filling out to 6-foot-2 and 185 pounds, he was spotted by Dave Gagner, the Canucks director of player development at the time, Coincidentally, Gagner had been Tanev's inline hockey coach years before.

In his only season at RIT, Tanev scored 10 goals and 28 points, was plus-33 and named Atlantic Hockey's Rookie of the Year.

He began his pro career with Manitoba of the American Hockey League in 2010-11. Over the next three seasons he also played for Chicago in the AHL.

Tanev's first full NHL opportunity arrived in the lockout-shortened 2012-13 season, when he played 38 of the Canucks' 48 games.

On March 24, 2015, Tanev signed a five-year contract.

Tanev signed a four-year contract with the Calgary Flames on Oct. 9, 2020. He was traded to the Dallas Stars on Feb. 28, 2024, in a three-team deal also involving the New Jersey Devils, and then sent to the Toronto Maple Leafs on June 29, 2024, after he had two assists in 19 Stanley Cup Playoff games. He signed a six-year, $27 million contract (average annual value of $4.5 million) with the Maple Leafs two days later.