[2] He began playing hockey in Maine around the age of three with his older brother, and would practice at home when the pond by the family house froze over in the winter.

During the summer after his sophomore year, Hathaway and his Bears teammate Mike Juola purchased and operated a lobster roll cart.

[10] Hathaway was part of a team of freshmen, also including Dennis Robertson, Matt Wahl, Marco de Filippo Roia, Mark Hourihan, and Jake Goldberg, that was expected to play a key role with the Bears in the 2010–11 season.

[13] At the end of the season, Hathaway was one of 23 Bears, including eight freshmen, named to the 2011 ECAC Hockey All-Academic Team, given to student-athletes with at least a 3.00 cumulative grade point average on a 4.00 scale.

[20] Following his junior year at Brown, Hathaway was invited to attend summer development camps with the Boston Bruins and Pittsburgh Penguins.

During the 2014–15 season, Hathaway played 72 games with Adirondack, where his 19 goals and 36 points impressed the Calgary Flames' general manager Brad Treliving.

[24] After spending much of the 2015–16 season with the Stockton Heat, Hathaway earned his first recall and made his NHL debut for the Flames on February 29, 2016, in a 4–3 loss to the Philadelphia Flyers.

[27] On November 18, 2019, Hathaway was given a match penalty and was ejected from a game against the Anaheim Ducks when he intentionally spat on skater Erik Gudbranson during a fight.