The Rangers sent a first-round pick in 2015 and a second-round pick in 2014 to Tampa Bay in the deal, which was completed in the final hours before Wednesday's 3 p.m. ET trade deadline.
There are two picks-related conditions in the trade. If the Rangers reach the Eastern Conference finals this season, the 2014 pick headed to Tampa Bay would become a first-round selection. If Callahan, a pending unrestricted free agent, re-signs with the Lightning, New York would receive a second-round pick in 2015 and Tampa Bay would get an additional seventh-round pick in 2015.
St. Louis made his Rangers debut Wednesday night against the Toronto Maple Leafs at Madison Square Garden. The Rangers lost 3-2 in overtime, but St. Louis got a nice ovation when he hopped over the boards for his first shift 38 seconds in, and he created a surge of excitement when he fired a hard shot on goal from the top edge of the left circle.
"I know this is going to be a challenge for me, but I love challenges and I like to rise to the occasion," St. Louis said after recording three shots in 20 minutes, 11 seconds of ice time. "This is a chance to play the game in one of the biggest markets, and I know what comes with it."
St. Louis requested a trade out of Tampa Bay after he was initially snubbed by general manager Steve Yzerman -- also the GM of Team Canada -- when his boss named the 2014 Olympic squad. St. Louis later was added as an injury replacement for the Lightning's Steven Stamkos and won a gold medal with Team Canada, but that apparently did not change the situation.
When asked if St. Louis had a hand in making the trade happen, Yzerman told reporters on Wednesday afternoon the two had "multiple" discussions about St. Louis' future with the franchise. However, Yzerman mostly deferred to St. Louis saying, "I'm not going to stand here and judge him."
St. Louis, who was named Tampa Bay's captain prior to this season, had a no-trade clause in his contract and reportedly told Yzerman that New York was his preferred destination. Yzerman acknowledged St. Louis' trade request in a written statement Wednesday.
"We'd like to thank Marty for everything he has done on and off the ice during his outstanding 13-year career in Tampa Bay," Yzerman said in the statement. "He has been one of the greatest players in the organization's history, but in the end we honored his request today. We wish him and his family the best of luck as he continues his career in New York."
St. Louis issued an open thank you letter to Lightning fans, in which he declined to explain his reasons for wanting a trade.
"Today is a bittersweet day for me," he wrote. "I am sad that this chapter of my career is over. I have had 14 wonderful years in Tampa and have cherished being a member of the Tampa Bay Lightning.