Robert Biedron is Poland's first openly gay mayor. The Polish lawmaker is pictured here being sworn in during the first session of the Polish parliament in Warsaw Nov. 8, 2011. REUTERS/Peter Andrews

Poland elected its first openly gay mayor Monday in what is being hailed as a major victory by LGBT rights campaigners. Robert Biedron, a gay rights activist, won a runoff election in the northern Polish city of Slupsk with 57 percent of the vote, according to Reuters.

Biedron, who had previously made history as the first openly gay member of Poland’s parliament, beat out Zbigniew Konwinski, a candidate from Poland’s ruling Civic Platform party in a surprise victory on Sunday. Having received only 20 percent of the vote in the first round of voting, Biedron had not been expected to win Sunday’s election. Local media attributed the victory to grassroots efforts by the candidate, who worked hard to gain support from voters he had served during his parliamentary tenure, reported Reuters. The election results were made public Monday.

The victory marks an important milestone for Poland, which remains one of the most devoutly Roman Catholic countries in Europe. Biedron has pointed to the success of his campaign as a sign of growing tolerance in the country. "I see how fast Polish society has learned its lesson of tolerance. So I am very optimistic and happy with Polish society, and proud," Biedron told the Associated Press in an interview before the election.

Biedron made a name for himself on the Polish political scene for founding Poland’s Campaign Against Homophobia, according to the LGBT news site Pink News. The group is known as one of the most successful LGBT rights groups in the former Soviet Union and for its success in developing community mobilization despite the conservative political setting it operates within, according to the Open Society Foundation.

While Biedron’s election may signal growing tolerance for gay rights causes in Poland, the country still has a recent record of rejecting initiatives in that direction. Last year, parliament defeated three draft laws that would have granted limited legal rights to gay couples in the country, according to Reuters.