Terms of the deal were not disclosed by the Devils but media reported it was an eight-year, $46 million contract.
Zajac missed all but 15 games of the 2011-12 regular season but returned in time to play a key role in the Devils' playoff run, scoring 14 points in the team's 24 postseason games.
"During his time in New Jersey, Travis Zajac has become a solid, all-situation player and one of the core leaders of our hockey club," Devils General Manager Lou Lamoriello said in a statement.
Zajac, who was selected by the Devils in the first round of the 2004 NHL Draft, missed most of last season with an Achilles injury but was in stellar form for the postseason.
With the Devils facing elimination in the opening round of last year's playoffs, Zajac scored an overtime goal that forced a decisive seventh game against the Florida Panthers.
