The twin brother of late president Lech Kaczynski, whose April 10 death in an air crash in Russia forced the early presidential ballot, Jaroslaw has consistently trailed liberal candidate Bronislaw Komorowski in opinion polls.
But the gap between the two main rivals has narrowed in recent weeks.
"Since president Lech Kaczynski's plane crash, Poland's conservative and openly Eurosceptic bishops and priests have thrown their support behind his twin brother," political scientist Kazimierz Kik told AFP.
With the church in Poland divided, part of the hierarchy, led by the country's new primate, Archbishop Jozef Kowalczyk, has called on the clergy to remain neutral.
"But on the other hand, there is the fundamentalist Radio Maryja broadcaster and a large section of the episcopate engaged directly in the campaign," he said.
Five clerics teaching at the John Paul II Catholic University in Krakow joined a "support committee" for Jaroslaw Kaczynski.
"Priests must not be active in political parties. But as a citizen, I am entitled to express my opinion," says one of them, Father Krzysztof Koscielniak.
"I gave my support to Kaczynski because he is a patriot, a responsible man, respectful of values that I espouse," he told Poland's Rzeczpospolita daily.
In a homily delivered in Wroclaw, the south-western city's Archbishop Marian Golebiewski called for "law and justice to reign" in Poland, a phrase which coincides with Kaczynski's conservative Law and Justice (PiS) opposition party.
Synergy between Church and party
"There is a synergy between the Catholic Church and Kaczynski's PiS party," said Kik.
"The church, which exercises its spiritual power mainly among Poland's conservative and disadvantaged social strata, is looking to expand its political influence. Jaroslaw Kaczynski, who has the same electorate, is likely to guarantee that influence," he observed.
"The Church's decision to bury the late president in Krakow's historic and prestigious Wawel Cathedral was an initial gesture toward the conservative opposition led by his brother," he added.
Support in collecting the signatures needed to endorse Kaczynski's candidature for president was another.
Instead of the 100 000 signatures required to register a candidate, Kaczynski gathered 1.6 million thanks to committees organised in the parishes, Kik said.