Mitchell, 26, played 23 games for the Leafs, with two goals and an assist, and was playing for the Marlies of the AHL.
The Rangers gave up a seventh-round pick for Mitchell, who may start off in Connecticut with Kris Newbury currently up as the 13th forward.
A very quiet day for the Rangers, who never got close enough with the Stars on Brad Richards to even have Dallas GM Joe Nieuwendyk ask Richards to waive his no-trade clause. Richards' camp never heard a thing from the Stars all day.
So the chase for Richards will resume on July 1, and the Rangers go forward as is.