Boston Bruins

Following completion of his collegiate career, Hunwick was then signed by the Boston Bruins to a two-year entry-level contract on June 26, 2007.^[8] Attending his first Bruins training camp, Hunwick was among the final cuts and assigned to American Hockey League affiliate, the Providence Bruins, to begin the 2007–08 season.^[9] After spending a month with Providence, Hunwick was recalled by Boston and played his first NHL regular season game in a 2–1 victory over the Buffalo Sabres on November 10, 2007. In his third recall to the Bruins, Hunwick recorded his first NHL point, an assist in a 2–1 defeat of the Toronto Maple Leafs on December 9.^[10] He finished his first professional season primarily with Providence, scoring 23 points in 55 games while totaling 13 games in the NHL from four separate recalls.

In the following 2008–09 season, Hunwick was again initially reassigned to the AHL but after only two games was recalled and remained with the Bruins for the majority of the campaign. He scored his first career goal against Vesa Toskala in a 3–2 win over the Toronto Maple Leafs on November 17, 2008.^[11] His goal sparked a six-game scoring streak which tied Hall of Fame defenseman, Ray Bourque, as a club record for rookie defenseman. On January 10, 2009, in a game against the Carolina Hurricanes, Hunwick got into his first NHL fight, one-punching to knock down Justin Williams.^[12] Establishing a puck-moving role among the Bruins defense corps, Hunwick amassed a career-high 21 assists and 27 points in 53 regular season games. Hunwick made his post-season debut with the Bruins in game one of the Eastern Conference Quarterfinals against the Montreal Canadiens on April 16, 2009. However, on April 18, at a team meeting before game two against the Canadiens, Hunwick complained of abdominal pain. After consultation with the team doctor, it was determined that he needed medical treatment and Hunwick was taken to the hospital via ambulance. He underwent emergency surgery for a ruptured spleen, and was ruled out for the remainder of the playoffs.^[13]

Hunwick opted out of salary arbitration and re-signed to a two-year contract with the Bruins on July 20, 2009.^[14] Recovered from his splenectomy, Hunwick played his first full NHL season in 2009–10, playing in a career high 76 games. Despite matching his six goals from the previous year, Hunwick regressed offensively and struggled to recapture his form throughout the year to be occasionally relegated as a reserve defenseman. He recorded an assist as his first career post-season point in game one of a series quarterfinals victory against the Buffalo Sabres.^[15] Succumbing to the Philadelphia Flyers in the Eastern Conference Semi-finals, Hunwick finished to appear in all 13 playoff games for 6 assists.

Colorado Avalanche

In the 2010–11 season, with the Bruins in need to reduce roster salary, Hunwick was traded to the Colorado Avalanche in exchange for Colby Cohen on November 29, 2010.^[16] On November 30, 2010, Hunwick made his debut for the Avalanche in a 3–2 overtime defeat.^[17] Hunwick's former team would go on to win the Stanley Cup that year.

On June 7, 2012 the Colorado Avalanche announced that they had re-signed Hunwick, to a two-year deal worth $3.2 million.^[18] In the final year of his contract and at the beginning of the 2013–14 season, Hunwick was relegated as a reserve defenseman and was placed on waivers by the Avalanche. Upon clearing, he was reassigned to the AHL for the first time since 2008 with affiliate, the Lake Erie Monsters on October 12, 2013.^[19]

New York Rangers

On July 1, 2014, Hunwick ended his four-year tenure with the Avalanche by signing as a free agent to a one-year contract with the New York Rangers.^[20] In the 2014–15 season, Hunwick returned to the NHL as the Rangers depth defenseman. He appeared in 55 games for 11 points and played 6 games in the post-season for the first time since 2010.

Toronto Maple Leafs

Hunwick was not re-signed by the Rangers and on July 1, 2015, he signed a two-year deal worth $2.4 million with the Toronto Maple Leafs.^[21] Head coach Mike Babcock played a big role in the signing. Babcock, impressed with Hunwick's work ethic upon seeing him at a gym in 2013, made a case for acquiring him.^[22]

Pittsburgh Penguins

In concluding a successful two-year tenure with the Maple Leafs, Hunwick left as a free agent and signed a three-year $6.75 million contract with two time reigning champions, the Pittsburgh Penguins, on July 1, 2017.^[23]

Buffalo Sabres

On June 27, 2018, Hunwick, along with teammate Conor Sheary, was traded to the Buffalo Sabres for a fourth-round pick in the 2019 NHL Entry Draft. In doing so, the Penguins cleared over $5 million in salary cap space.^[24]