Midfielder Ewelina Kamczyk opened the scoring for Poland with a long-range lob 17 minutes into the match in the Baltic city of Gdańsk, Polish state news agency PAP reported.
Adriana Achcińska put the score at 2-0 in Poland's favour three minutes later, converting a pass from captain Ewa Pajor.
The home win marked a strong start to Poland's Nations League campaign and a promising lead-up to the Euro 2025 tournament later this year.
The Poles, the top seeds in League B Group 1, are ranked 28th worldwide by football's governing body FIFA, while Northern Ireland are No. 44 in the FIFA table.
Manager Nina Patalon's squad will take on Romania in Bucharest on Tuesday in their next Nations League fixture.
Poland have been drawn to play Germany, Sweden and Denmark in the group stage of this year's European football championships in Switzerland.
Poland head coach Nina Patalon. Photo: PAP/Adam Warżawa
The Polish team opens its Euro 2025 campaign against Germany on July 4.
Poland captain Ewa Pajor. Photo: PAP/Adam Warżawa
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Source: IAR, PAP, pzpn.pl