Hayes chose to defer his professional career and followed his older brother Jimmy, playing four seasons with the Boston College Eagles.

In the first year of his new contract, Hayes was the recipient of the teams' Gene Hart Memorial Award as the player who displays the most "heart".

"[1] Hayes' South Shore teammates included future NHL players Noel Acciari, Chris Wagner, and Charlie Coyle.

[4] After scoring one goal and two assists in an exhibition game against the University of Toronto,[5] Hayes recorded his first NCAA career point on October 15, 2010, in a 6–2 win over the Denver Pioneers.

[12] Then, in a February 26, 2013 match against UMass Lowell River Hawks, Hayes sustained an injury to a leg and lost consciousness in the locker room.

He told the Boston Herald, "I think I always knew how important the game was to me, but I think I had to somewhat grow up a bit and take my body serious, take my school serious, take my strength and conditioning serious, and just a mixture of those three kind of allowed me to be the player I am today.

[19] The Blackhawks, meanwhile, received a second-round compensatory pick in the 2015 NHL Entry Draft, which eventually was used to select Graham Knott.

[22] He made his NHL debut with the Rangers on October 12, 2014, in a home game against the Toronto Maple Leafs, playing alongside Carl Hagelin and J. T. Miller.

[23] A few games later, while centering a line with Rick Nash and former Boston College teammate, Chris Kreider, Hayes scored his first career NHL goal against the San Jose Sharks.

[24][25] He finished the regular season ranking fifth among all league rookies in both points and assists as the Rangers qualified for the 2015 Stanley Cup playoffs.

[27] As the Rangers advanced through the playoffs, he scored the game-tying goal in an eventual overtime win over the Washington Capitals in the second round, and recorded an assist on Dominic Moore's late third period winner in game one of the Eastern Conference Final against the Tampa Bay Lightning.

[26] While attending the Rangers' training camp before the 2015–16 season, head coach Alain Vigneault said he had decided to give Hayes a chance on the first line with Kreider and Derek Stepan.

[38] In 12 appearances at the 2017 Stanley Cup playoffs, Hayes recorded 0 goals and 3 assists,[39] and the Rangers were eliminated in game six of the second round against the Ottawa Senators.

[47] Later that month, while playing on a line with Kyle Connor, Hayes helped the Jets qualify for the 2019 Stanley Cup playoffs.

[51] The trade to Philadelphia meant a reunion for Hayes and Vigneault, who was hired as the Flyers head coach after being fired from the Rangers in 2018.

[52][53] After a strong training camp performance on a line with James van Riemsdyk and Oskar Lindblom, Hayes made his debut in a preseason loss against the New York Islanders.

He was named a finalist for the Bill Masterton Memorial Trophy, awarded to the player who "best exemplifies the qualities of perseverance, sportsmanship and dedication to hockey.

"[67] On June 27, 2023, the Flyers traded Hayes at 50% retention to the St. Louis Blues in exchange for a sixth-round selection in the 2024 NHL Entry Draft.

[68] On June 29, 2024, Hayes was traded, along with a second-round selection in the 2025 NHL Entry Draft to the Pittsburgh Penguins for future considerations.

"[71] Hayes and his brother Jimmy were both selected to represent the United States national team at the 2014 IIHF World Championship in Minsk, Belarus.

[38] Hayes was selected to represent the United States again at the 2017 IIHF World Championship where he played on a line with collegiate teammate and friend Johnny Gaudreau.

[77] His closest friend in the NHL was former Boston College teammate Johnny Gaudreau, who was killed by a drunk driver on August 29, 2024[79][81] Hayes served as a pallbearer at his funeral.