The 41-year-old forward, who spent the lockout-shortened 2012-13 campaign with the Dallas Stars and Boston Bruins, received a one-year deal worth $2 million with another $2 million available in bonuses, The Bergen (N.J.) Record reported.
The Devils signing comes after Jagr played a key role in propelling the Bruins to the Stanley Cup Finals with 10 assists in 22 playoff games. Boston obtained him from the Stars at the trading deadline.
The Czech veteran netted 16 goals and 19 assists for 35 points in 45 games with the two teams during the regular season.
Over 1,391 regular-season games with the Pittsburgh Penguins, Washington Capitals, New York Rangers, Philadelphia Flyers, Dallas and Boston, Jagr has racked up 681 goals and 1,688 points -- eighth-most in NHL history.
The Devils signed him after high-scoring Ilya Kovalchuk this month retired from the NHL with 12 years and $77 million remaining on his contract, returning to his native Russia to play in the Kontinental Hockey Association.