According to TSN of Canada, Shanahan signed a contract worth $800,000 on Wednesday, but the actual amount will be pro-rated for the remaining portion of the current season.
The club originally announced on Saturday that Shanahan had agreed in principle to return to the team for whom he began his 21-year career.
Devils general manager Lou Lamoriello said there is no firm timetable for Shanahan's return to game action, but added that the veteran will skate on his own for the time being.
A native of Mimico, Ontario, the soon-to-be 40-year-old was the Devils' second overall pick in the 1987 draft. After four seasons with New Jersey, he signed with the St. Louis Blues as a free agent in July, 1991 -- a move which altered the luck of the franchise -- as the Devils received defenseman Scott Stevens as compensation.
Shanahan leads all active NHL players in goals scored with 650, ranking 11th on the all-time list, only 18 behind Hall of Fame forward Luc Robitaille. He has also appeared in eight All-Star games and captured three Stanley Cup titles while with the Red Wings in 1997, 1998 and 2002.
With the New York Rangers a season ago, his second on Broadway, Shanahan posted 23 goals and 46 points in 73 games.