Amateur Zajac began his
junior ice hockey career with the
Salmon Arm Silverbacks of the
British Columbia Hockey League (BCHL). One of his teammates was
Brady Murray, who would briefly play in the NHL for the
Los Angeles Kings, and his linemate was future
Calgary Flames winger
Kris Chucko. In his second season with Salmon Arm, Zajac led the team in goals, assists and points, At season's end, he was named the
MVP of the BCHL's Interior Division, and he played in the BCHL All-Star Game. His play attracted attention, and he was projected to be a potential first-round draft pick in the
2004 NHL entry draft. The projection proved accurate, as the
New Jersey Devils would take him with the 20th overall pick. The Devils traded up to get Zajac, which "mean[t] a lot" to him, but was not a surprise, as the Devils scouted him more than any other team. Then-Devils General Manager
Lou Lamoriello commented that there would be room for Zajac on the North Dakota roster because the Devils were recalling forward
Zach Parise, drafted
the year earlier, to play professional hockey. He added two more in the semifinal game against the
University of Minnesota as the Sioux won 4–2. Although the Sioux lost to the
University of Denver in the championship game, Zajac tallied a power-play goal to tie the game. Despite the loss, he was named to the Championship All-Tournament Team, as well as the NCAA East All-Tournament Team and the
Western Collegiate Hockey Association (WCHA) All-Rookie Team. The following year, Zajac finished the season with 18 goals and 29 assists for 47 points. That season, the Sioux featured several future NHL players, including
Taylor Chorney,
Brian Lee,
T. J. Oshie,
Chris Porter,
Matt Smaby,
Drew Stafford and
Jonathan Toews. The Sioux won the
Broadmoor Trophy as the WCHA playoff champion, and advanced once again to the
NCAA tournament.
Professional New Jersey Devils (2006–2021) After North Dakota's season was over, Zajac signed an entry-level contract with the Devils, forgoing his last two seasons of college eligibility. He scored one assist and earned two penalty minutes in two appearances with the Devils'
American Hockey League (AHL) affiliate, the
Albany River Rats. Despite being considered to have an outside chance at making the Devils' roster out of
training camp, Zajac survived the first round of cuts and eventually made it to the roster on opening night of the
2006–07 season. He scored his first career NHL goal in the second game of the season against the
Dallas Stars. Zajac was placed on the Devils' second line with former North Dakota standout Zach Parise and veteran winger
Jamie Langenbrunner. owing to
Zajac and
Zach's initials and Langenbrunner's veteran status ("
Pop(s)"). Zajac would miss two games in October due to a leg injury; Zajac would net three assists against the
Ottawa Senators in a November game. Later in the season, Zajac notched his first NHL two-goal game against the
Philadelphia Flyers, and had an eight-game point streak in late March. In Game 1 of the Semifinals against Ottawa, Zajac would score his first career post-season goal; the Senators, however, won the game 5–4. Although Zajac earned an assist on linemate Langenbrunner's
overtime goal in Game 2, Zajac finished tenth in voting for the
Calder Memorial Trophy, awarded to the NHL's rookie of the year, and won the Devils' Fan Club award for Rookie of the Year. At the start of Zajac's
sophomore season, he was still centering the second line with Zach Parise;
Brian Gionta replaced Langenbrunner on right wing while the latter recovered from sports hernia surgery. Zajac scored his first goal of the season in the team's fifth game against the
Atlanta Thrashers, a 6–5 Devils win. In October, he was moved up to the top line, centering Gionta and Eliáš, and saw an increase in time on the power play unit. January 2008 was a good month for Zajac – he had a four-game point streak, during which he tied his career high with a three-point game (three
assists) against the Flyers. During the subsequent off-season, Zajac signed a multi-year contract extension with the Devils, avoiding salary arbitration. The
2009–10 season was one of many milestones for Zajac; he notched his 100th career assist in November, his 200th career point in March and appeared in his 300th game in February. He once again led the team in faceoffs, winning 52.9% of his draws. Zajac had high expectations heading into
his fifth season. Replacing Langenbrunner on the top line was
Ilya Kovalchuk, whom the Devils acquired at the trade deadline the previous year in a blockbuster trade, and re-signed to a controversial 15-year deal in the off-season. Parise wanted Zajac to shoot more, saying he had "one of the best shots on [the] team." Zajac's productivity took another hit when Parise
tore his meniscus and was sidelined for several months. Further injuries and poor play forced Head Coach
John MacLean to shuffle his lines further; Zajac's linemates for the first half of the season included Parise, Langenbrunner, Kovalchuk, Zubrus,
Brian Rolston,
David Clarkson, Eliáš and
Adam Mair. Despite the lack of stability for his wingmen, Zajac's faceoff ability continued to improve. He credited Assistant Coach
Adam Oates, considered one of the premier faceoff men of his era, with the improvement. Following the firing of MacLean and the trading of captain Langenbrunner, the Devils found themselves playing better under returning Head Coach
Jacques Lemaire. Zajac snapped a five-game pointless streak, and shortly thereafter scored a short-handed goal and added three assists in just three games. On March 15, Zajac tied
Ken Daneyko's team record for consecutive games played (388); he broke the record the following game against Ottawa. Although the Devils did not qualify for the
2011 playoffs, Zajac won the team's Unsung Hero award. , April 2011 On April 24, 2012, Zajac scored his second career overtime goal against the
Florida Panthers in Game 6 of the Eastern Conference Quarterfinals, to force a Game 7, which the Devils also won in double Overtime. Hw re-signed with the Devils in January 2013, committing to an eight-year, $46 million contract. He recorded his first career
hat-trick against Florida Panthers on March 31, 2014. While the
2017–18 season brought the Devils back to the Stanley Cup playoffs for the first time since 2012, he played his fewest games since the 2012–13 season due to a
pectoral injury that required surgery. He played his 1,000th career game for the Devils against the
Washington Capitals on February 21, 2021. On March 30, 2021, during a game against the
Boston Bruins, Zajac scored his 200th career goal.
New York Islanders (2021) During the pandemic-delayed
2020–21 season, while in the final season of his eight-year contract and his 15th season within the Devils organization, on April 7, 2021, Zajac was traded to the
New York Islanders along with
Kyle Palmieri, in exchange for a first-round pick in the
2021 NHL entry draft, a conditional
2022 fourth-round pick, and forwards
A. J. Greer and Mason Jobst.
Retirement On September 20, 2021, Zajac signed a one-day contract to retire with the Devils. Zajac was honored during a Devils game against the Winnipeg Jets on March 10, 2022, for playing 1,000 games with the team, where he also performed a ceremonial puck drop. ==International play==