As a youth, Hayes played in the 2004 and 2005 Quebec International Pee-Wee Hockey Tournaments with a minor ice hockey team from South Shore. Hayes played for Noble and Greenough School before joining the Boston College in the NCAA's Hockey East conference between 2011 and 2014. During his first three seasons in the NCAA, he produced small but effective numbers, recording 17 goals and 50 assists for 67 points over that time, and was a member of the 2012 National Championship team. However, he emerged as a star player in his final, senior year, where he played on a line with current Calgary Flames players Bill Arnold and Johnny Gaudreau, the latter of which was the Hobey Baker Award winner in 2014. Hayes nearly doubled his point production from his first three seasons scoring 27 goals, and 38 assists for 65 points. He earned a top ten nomination for the Hobey Baker Award and earned a reputation as a large, two-way player with a prolific shot and power play effectiveness. Hayes was also named MVP of the 2014 Beanpot tournament.
Professional
New York Rangers
The rights that the Chicago Blackhawks held to Hayes expired on August 15, 2014, without Hayes having signed with the team. On August 16, Hayes became an unrestricted free agent, after which on August 20, he signed with the New York Rangers on an entry-level contract. As a result of his signing elsewhere, the Blackhawks received a second-round compensatory pick in the 2015 NHL Entry Draft. On October 19, 2014, in a 4–0 Rangers win over the San Jose Sharks, Hayes scored his first career NHL goal. He finished the season with 17 goals and 28 assists for 45 points. Hayes regressed slightly during the 2015–16 season, recording only 14 goals and 22 assists for 36 points. Despite this, the Rangers signed him to a two-year, $5.2 million contract extension Hayes improved in the 2016–17 season, scoring 17 goals and 32 assists for 49 points. Throughout the season, he centered a highly-effective third line with Michael Grabner and J. T. Miller. On July 31, 2018, as a restricted free agent, Hayes re-signed with the Rangers to a one-year contract.
Winnipeg Jets
In the 2018–19 season, his fifth with the Rangers, Hayes increased his offensive output in contributing with 42 points in 51 games. While in his final year under contract before free agency and with New York out of playoff contention, Hayes was traded at the NHL trade deadline to the Winnipeg Jets in exchange for a first-round pick in the 2019 NHL Entry Draft, Brendan Lemieux and a conditional fourth-round pick in the 2022 NHL Entry Draft on February 25, 2019. On March 1, 2019 Hayes scored his first goal as a Jet in a 5–3 win over the visitingNashville Predators. Hayes also recorded two assists in the game and was named the game's third star.
Philadelphia Flyers
On June 3, 2019, Hayes' negotiating rights were traded to the Philadelphia Flyers in exchange for a fifth-round draft pick in the 2019 Entry Draft. On June 19, the Flyers signed Hayes to a seven-year, $50 million contract with an annual average of $7.14 million.
Kevin Hayes grew up with older brother Jimmy in Dorchester, Massachusetts, and the brothers both attended Noble and Greenough School. Jimmy is also a professional ice hockey player, most recently in the Pittsburgh Penguins organization. The Hayes brothers are cousins with former NHL players Tom Fitzgerald and Keith Tkachuk, as well as Tkachuk's sons, current NHL players Matthew and Brady, and Fitzgerald's sons Ryan, a Boston Bruins draft pick, and Casey, a member of Boston College's Eagles. At the start of the 2019-20 NHL season, Hayes was named an alternate captain of the Flyers. Hayes has beer named after him called "Big Hayse-y." It is sold at Yards Brewing Company in Philadelphia, Pennsylvania.
