Financial terms were not disclosed, but ESPN.com's Pierre LeBrun reports that Palat's deal is worth $10 million, with him receiving $2.8 million next season, $3.2 million in 2015-16 and $4 million in 2016-17. Palat was set to become a restricted free agent on July 1.
Palat, 23, played in 81 games this past season, scoring 23 goals and recording 36 assists, leading the team with a +32 rating.
Palat is a finalist for the Calder Trophy, given to the league's top rookie, and among rookies was ranked second in points and third in goals.
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Palat was originally selected by the Lightning in the seventh round, 208th overall, at the 2011 NHL Draft.