Poland's left-wing parties on Tuesday approved Robert Biedron, an openly gay politician, as their candidate in the May presidential election.
The move in the conservative, predominantly Catholic country where same-sex unions are not recognised, was aimed at preserving democracy, they said.
Leaders in the Lewica (Left) alliance said they chose Biedron because of his clear backing for women's rights, the rule of law and the separation of church and state, all of which have been undermined by the governing right-wing Law and Justice (PiS) party since it took office in 2015.
Biedron "has clear views on the secular state, on social affairs, on the EU, on matters of freedom, including women's issues," said Wlodzimierz Czarzasty, leader of the Democratic Left Alliance (SLD).
Biedron, 44, will face incumbent right-wing President Andrzej Duda who is tipped as the favourite in the race and backed by the governing PiS, which is known for strident anti-gay rhetoric.
He will also run against liberal candidate Malgorzata Kidawa-Blonska backed by the Civic Platform (PO), the leading opposition party and seen as Duda's main rival.
Biedron is the leader of Wiosna (Spring), one of three left-wing parties in the Left alliance that entered the Polish parliament in October's general election, winning 49 of the 460 seats, after a four year absence.
Currently a member of the European Parliament, Biedron previously served as a Polish MP and mayor of the northern town of Slupsk.
He has long campaigned for gay rights, including the formal recognition of gay partnerships.
Biedron also vowed to close all coal mines by 2035 in a bid to stem chronic smog in the coal-dependent country.