Matty Cash opened the scoring in the 27th minute at the Silesian Stadium in Chorzów, southern Poland, before captain Robert Lewandowski doubled the lead in first-half stoppage time.
Jakub Kamiński made it 3-0 in the 54th, while Benjamin Kallman pulled one back for Finland in the 88th.
The win provided a lift for Poland under their new coach Jan Urban, following a 1-1 draw with the Netherlands in their previous qualifier on Thursday.
Poland are ranked 37th worldwide by football's governing body FIFA, while Finland are No. 69.
After five rounds of qualifiers, Poland sit second in Group G with 10 points. The Netherlands top the group with 10 points from four games and an 14-3 goal difference, putting them ahead of Poland.
Poland will next face Lithuania away on October 12.
The group winner advances directly to the World Cup, while the runner-up moves to the play-offs.
The 2026 World Cup will be held in June and July next year in the United States, Canada and Mexico.
Poland reached the round of 16 at the 2022 World Cup in Qatar before being eliminated by eventual runners-up France.
(gs)
Source: IAR, PAP, pzpn.pl