"My song says that dreams are most important and can help everyone achieve anything," Węgiel said after the verdict had been announced. She greeted Poland and thanked Belarus for organising the competition.
The 13-year-old singer had earlier won the first season of The Voice Kids Poland talent show.
A record number of 20 countries took part in this year's Junior Eurovision contest, including debuting Kazakhstan and Wales.
The winner was selected by a vote of the jury and television viewers. The Polish singer won 215 points in total.
The Junior Eurovision has been organised since 2003 for singers aged 9-15. The contest was hosted by Belarus for the second time. Poland won the competition for the first time having participated in the event five times. (PAP)
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