Prokop, 19, made the announcement in an Instagram post.
"It has been quite the journey to get to this point in my life, but I could not be happier with my decision to come out," Prokop wrote. "From a young age I have dreamed of being an NHL player, and I believe that living my authentic life will allow me to bring my whole self to the rink and improve my chances of fulfilling my dreams."
No NHL player, active or retired, has come out publicly.
Prokop, a 6-foot-4 right-handed defenseman from Edmonton, Alberta, was selected in the third round by the Predators in the 2020 NHL draft. He signed a three-year entry-level contract with the Predators in December and played last season for the Calgary Hitmen of the Western Hockey League, where he was an alternate captain.
He told ESPN that he struggled last season and wanted to come out publicly because he believed it would help ease his mind and allow him to play his best hockey.
Prokop said he made his decision to come out in April when he returned from Calgary after his season ended because of COVID-19.
"I was lying in bed one night, had just deleted a dating app for the fourth or fifth time, and I was extremely frustrated because I couldn't be my true authentic self," Prokop told ESPN. "In that moment I said, 'Enough is enough. I'm accepting who I am. I want to live the way I want to, and I want to accept myself as a gay man.'"
Prokop began coming out to some family members and teammates this past year and told Predators management he was gay in June. He said the Predators have been extremely supportive of him, including the first person he talked to from the team: assistant general manager Brian Poile.
"He in that moment showed me a lot of support and told me the Predators are behind me 1,000% and want what's best for me and that they're proud of me during this," Prokop told ESPN. "I remember getting off that phone call and tears just started coming from my eyes, I was so excited. And in that moment, I thought, this is what it's going to feel like for the rest of my life. For them to show that support that they did in that moment, it felt like I can rule the world."
"The Nashville Predators organization is proud of Luke for the courage he is displaying in coming out today and we will support him unequivocally in the days, weeks, and years to come as he continues to develop as a prospect," Predators president and CEO Sean Henry said. "A long-stated goal in our organization is equality for all, including the LGBTQ community, and it is important that Luke feels comfortable and part of an inclusive environment as he moves forward in his career."
Said Josi: "Our message as a team [is that] we're obviously very supportive of him. We just reached out and told him [we'll help with] whatever he needs and that we're proud of him. It's a big step for him, and we fully support him."
Prokop said his decision to come out was made independently of Carl Nassib's announcement in June, though Prokop found Nassib's words, and the reaction to his announcement, inspiring. Nassib, a defensive end for the Las Vegas Raiders, became the first active NFL player to come out as gay.
One fear for Prokop was that people would assume he is making his announcement for attention. However, one of the biggest reasons he wanted to come out was to live authentically. Last season, he often had to hide his phone from teammates at the rink.
In his statement, Prokop thanked his "amazing family, friends and agents -- who have known this about me and met me with love and support every step of the way."
"I hope that in sharing who I am I can help other people see that gay people are welcome in the hockey community, as we work to make sure that hockey is truly for everyone," Prokop wrote. "I may be new to the community, but I am eager to learn about the strong and resilient people who came before me and paved the way so I could be more comfortable today."
The NHL has worked to be an ally for the LGBTQ+ community for more than a decade. Players from all 31 teams have wrapped their sticks in rainbow tape for Pride Night events. Several players, including Calgary Flames captain Mark Giordano and Vancouver Canucks goalie Braden Holtby, and executives such as Pittsburgh Penguins president of hockey operations Brian Burke and Toronto Maple Leafs general manager Kyle Dubas have marched in local Pride parades.
In 2013, the NHL and NHL Players' Association partnered with You Can Play, an organization that "works to ensure the safety and inclusion of all in sports -- including LGBTQ+ athletes, coaches, and fans."
"As NHL players, we all strive to contribute toward helping our teams achieve success on the ice. Any player who can help in those efforts should be welcomed as a teammate," defenseman Ron Hainsey, then an NHLPA executive board member, said at the time. "This partnership solidifies the message that the hockey community believes in fairness and equality for everyone."
Since Prokop came out to Predators management, he said he has received support behind the scenes from the NHL. He said NHL commissioner Gary Bettman called him recently and told him to reach out anytime.
"I share his hope that these announcements can become more common in the hockey community," Bettman said in a statement. "LGBTQ players, coaches, and staff can only perform at their absolute best if they live their lives as their full and true selves. We do not take the meaning and importance of this announcement lightly."
Bettman added that the NHL wants to give Prokop a "welcoming and affirmative" experience and that the league will support any other players who would follow "in his trailblazing footsteps."
NHLPA executive director Don Fehr also lauded Prokop for his announcement.
"We know the NHL hockey community will support Luke as he strives toward his goal of playing in the NHL, and we applaud the example he is setting for those in the game of hockey and beyond," Fehr said in a statement.
Prokop said "it's hard to put into words" what it will mean to skate in a game next season, knowing his truth is out there.
"I'm going to lace up my skates the same. I'm going to put my jersey on the same, strap up my helmet, put on my gloves," Prokop said. "But I'm finally going to be able to breathe and exhale and show the world the real me. And I'm so excited to see where that can take me, not only as a hockey player but as a person as well."