Vainonen, 19, spent his first season with the Kingston Frontenacs in the CHL, and the native of Finland was fourth among defencemen with 22 points. He also was the captain of Finland's team at the 2012 U-18 World Championships.
He was the Predators' sixth selection in the 2012 draft at No. 118 overall in the fourth round.
I'm very excited about what happened today. We've worked on this deal with Toronto for a month, or over a month. It got a little bit of legs on draft day, but it really heated up last night, and we were able to complete the deal today.
— Penguins GM Jim Rutherford on Phil Kessel, who he acquired from the Maple Leafs in a trade on Wednesday