As a youth, Czarnik played in the 2005 Quebec International Pee-Wee Hockey Tournament with the Detroit Compuwareminor ice hockey team. Czarnik played four seasons of NCAA Division I hockey for the Miami RedHawks. In his sophomore year at Miami University, Czarnik's outstanding play was rewarded with a selection to the 2012–13 CCHA All-Conference First Team. On June 24, 2013, prior to the start of his junior season, Czarnik was named captain of the RedHawks by head coachEnrico Blasi. He held this position through the end of his senior season. Days after Miami was eliminated from the 2015 NCAA Division I Men's Ice Hockey Tournament and his college career had come to a close, Czarnik signed an entry-level deal with the Boston Bruins on March 31, 2015. He was assigned to the Bruins' AHL affiliate, the Providence Bruins. Prior to the 2016–17 NHL season, Czarnik made the Boston Bruins' roster out of training camp, making his NHL debut on October 13 for the Bruins' 6–3 win over the Columbus Blue Jackets. However, after two scoreless games and one healthy scratch with Boston, he was reassigned to Providence on October 20. However, following an elbow injury to David Backes, Boston recalled Czarnik on October 26. During a game that same day, Czarnik tallied his first NHL goal against the New York Rangers' Henrik Lundqvist in a 5–2 loss for the Bruins. On July 18, 2017, Czarnik was signed by the Bruins to a one-year contract to play in the 2017–18 season. Czarnik participated in the Bruins training camp prior to the 2017–18 season, and made the opening night roster out of camp but was reassigned to the Providence Bruins after playing in two games. Czarnik and teammate Jordan Binnington were named the Providence Bruins representatives at the 2018 AHL All-Star Classic. He was later named to the AHL Second All-Star Team. After playing in 10 games with the Bruins during the 2017–18 season, Czarnik was reassigned to the AHL on February 10, where he remained for the rest of the season. On July 1, 2018, having seen his career stall within the Bruins organization, Czarnik left as a free agent and secured a one-way, two-year, $2.5 million contract with the Calgary Flames. He made the Flames opening night roster out of training camp.
