As a youth, Zalewski played in the 2005 Quebec International Pee-Wee Hockey Tournament with a minor ice hockey team from Syracuse, New York. He later played one season with the Syracuse Stars of the Eastern Junior Hockey League. Zalewski was drafted 122nd overall by the Youngstown Phantoms in the USHLentry draft, but did not sign with the team. This was followed by two seasons in British Columbia with the Vernon Vipers of the BCHL. He committed to playing Division Icollege hockey for the Rensselaer Polytechnic Institute in 2010 while playing with the Vipers. After leaving the BCHL following the 2011–12 season, Zalewski attended the Rensselaer Polytechnic Institute where he played two seasons of NCAA Division I hockey with the RPI Engineers, registering 21 goals, 26 assists, 47 points, and 75 penalty minutes in 71 games. In his freshman season, he led all first year players on the team with 21 points as he helped the Engineers qualify for the ECAC Hockey Quarterfinals. On March 14, 2014, the Vancouver Canucks of the NHL signed Zalewski as a free agent to an entry-level contract. On April 12, 2014, Zalewski made his NHL debut, skating 11:47 with the Vancouver Canucks in a 5-2 loss to the Edmonton Oilers. On July 8, 2015, with Zalewski unable to retain an NHL contract with the Canucks, he opted to remain within the organization by signing a one-year AHL contract with the Utica Comets, an affiliate. On January 20, 2016, Zalewski signed a two-way, one year NHL contract with the Vancouver Canucks and was recalled the same day. As a free agent, Zalewski left the Canucks' organization after three full seasons, signing a one-year deal abroad with a German outfit, the Straubing Tigers of the DEL, on July 17, 2017. In doing so, he linked up with his brother Steven, who had become a member of the Tigers two years previously. In the 2017–18 season, Zalewski made a seamless transition to the DEL, contributing on the Tigers scoring line with 14 goals and 31 points in 51 games. With the conclusion of his contract with Straubing, Zalewski opted to leave as a free agent and agreed to a one-year contract to continue in the DEL with Kölner Haie on July 5, 2018. On August 22, 2019, Zalewski moved to the neighbouring Austrian Hockey League, agreeing to a one-year contract with the Vienna Capitals.
Personal
One of Zalewski's brothers, Steven, plays professional hockey as well, including time with both New Jersey and San Jose of the NHL. Another brother, Rich, played professionally in the Southern Hockey League. One of his sisters, Annika, plays college hockey for Colgate.
