The 26-year-old Ireland international started all nine of Leinster's games as they became the first side to retain the trophy thanks to their crushing 42-14 final victory over Ulster at Twickenham on Saturday.
Kearney scored six tries in total during the campaign, and proved the matchwinner in the semi-final win over Clermont Auvergne by setting up Cian Healy's try and slotting a monster drop goal.
He succeeds team-mate Sean O'Brien as the winner of the award.
Kearney said: "This is a massively proud moment for me. To be recognised for your performances throughout the season is a dream come true especially when it's in a European context.
"While I'm delighted with the recognition, an individual player is powerless without the support of his teammates. So I owe this award to the Leinster squad, to the management and to the all staff at the club."
Kearney and his team-mates will look to complete the double when they face the Ospreys in Sunday's RaboDirect Pro12 final.
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
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Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
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The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
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The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
