"We have to pull out, on that issue there is not a doubt," Kaczynski said in the final television debate ahead of Sunday's run-off vote, in which he is trailing in the polls behind the liberal Bronislaw Komorowski.
Komorowski has already made withdrawing Poland's troop contingent from Afghanistan within two years a key campaign pledge.
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Kaczynski did not specify a timeframe for the withdrawal, but said he had discussed the prospect during recent talks with British Prime Minister David Cameron.
"In the course of his mandate, and if I am elected then within my mandate also, the two armies will definitely withdraw from Afghanistan. We cannot stay there eternally," Kaczynski said.
Polish presidents are elected for five years.
Poland is one of the leading contributors to NATO's 142,000-strong International Security Assistance Force in Afghanistan. Its contingent is due to grow to 2,600 later this year.
Nineteen Polish soldiers have been killed in Afghanistan. The latest, sapper Pawel Stypula, 26, perished on Saturday in a boobytrap explosion.
Sunday's run-off ballot comes after Komorowski topped a June 20 first round but failed to clear the 50 percent hurdle to win outright. Opinion polls have repeatedly given him the edge.
The election was forced after president Lech Kaczynski -- Jaroslaw Kaczynski's twin brother and close political ally -- was killed in a plane crash in Russia in April.
