During the 2011–12 season, Athanasiou was one of five players to score 20 or more goals on a London Knights team that finished with the OHL's best record.

Athanasiou skated in nine of the Knights' first 17 playoff games as London reached the conference finals and recorded one goal and 3 assists.

Athanasiou was the fourth-leading scorer for the Colts, finishing third on the team with 29 goals and recording 38 assists in 66 games.

Athanasiou joined the Detroit Red Wings' AHL affiliate Grand Rapids Griffins during the Calder Cup playoffs but did not appear in any games.

Athanasiou made his NHL debut for the Red Wings on November 8, 2015, in a game against the Dallas Stars.

During the 2015–16 season, Athanasiou recorded nine goals and five assists in 37 games for the Red Wings, while averaging 9:01 of ice time.

[6] On October 21, 2017 - following a contract holdout to begin the season - Athanasiou and the Red Wings agreed to terms on a one-year deal worth $1,387,500.

In return for the post-season, Athanasiou went scoreless in four games as the Oilers failed to make it through the play-in round and missed the playoffs.

[12] As a free agent from the Kings, Athanasiou joined his fourth NHL team after signing a one-year, $3 million contract with the Chicago Blackhawks on July 13, 2022.