Ward, a member of the Stanley Cup champion Carolina Hurricanes last season, was in the first year of a two-year deal with New York that pays him US$2.75 million in each season.
The Rangers received defenceman Paul Mara from the Bruins. New York also sent newly acquired forward Pascal Dupuis to the Atlanta Thrashers for a third-round draft pick and prospect Alex Bourret shortly before the NHL trading deadline.
Dupuis, earning $790,000 this season, came to New York on Feb. 9 in a deal with the Minnesota Wild for forward Adam Hall.
The Bruins made one other trade before time ran out Tuesday, sending forward Brad Boyes to St. Louis for defenceman Dennis Wideman.
Ward was benched Saturday night in the Rangers' final game before Tuesday's NHL trading deadline, and coach Tom Renney said then it was not because the defenceman was about to be dealt. Renney said he wanted Ward on the team when the defenceman became a free agent last summer and still wanted to keep him.
But Ward left New York after posting three goals and 10 assists in 60 games this season. He became prone to mistakes over the course of the season, and Renney said the benching was to get him to take a step back and watch for a game.
Over the weekend reports surfaced that Ward and Jagr had a heated dispute on the bench during a 3-2 loss at Tampa Bay on Feb. 3.
"I've got no problem with anybody," Jagr told the Daily News. "He didn't play the last game and it's my fault? I don't think there's a problem in the locker room at all. I don't believe that he's going to the media for that.
"During the game there are a lot of situations. He wasn't happy, probably with the way I was talking to him. Should I write an e-mail? No."
Ward, a two-time Cup champion with Detroit, has 34 goals and 78 assists in 612 career games.
Mara had three goals and 15 assists in 59 games this season with Boston. He has played in 483 NHL games, also spending time with Phoenix and Tampa Bay.
He is earning $3 million this season and is signed at the same amount for the 2007-08 campaign.
The Rangers and Bruins entered play Tuesday tied for 11th place in the Eastern Conference, seven points and three spots below the playoff cutoff.