The 23-year-old burst onto the international scene this year by taking an extraordinary 26 wickets at an average of a mere 18.38 apiece in just three Tests with his unique brand of spin bowling, including the 'carrom ball', which helped see his country to a series win over India.
Mendis, who topped the voting for his award ahead of a 25-strong voting academy from a trio of pace bowlers in Stuart Broad (England), Morne Morkel (South Africa) and India's Ishant Sharma, after being nominated by a panel chaired by former West Indies captain Clive Lloyd, also starred in one-dayers.
In eight one-day internationals during the voting period, he took 20 wickets at 10.25.
"I am delighted to win the award," said Mendis after being presented with his trophy by Sri Lanka captain Mahela Jayawardene.
"It is an honour to play for Sri Lanka and I hope to continue playing for my country for a long time to come."
The Emerging Player of the Year Award was one of eight individual prizes given at this year's awards.
Players eligible for this award must be under 26 years of age at the start of the voting period (August 9 2007) and have played no more than five Test matches and/or 10 ODIs before the start of the voting period.