The nightclub owner, entrepreneur and LGBT rights activist won a seat on Warsaw city council last month.
The Green party member ran on a Social Democrat ticket.
Mr Legierski, who is black, has suffered racism and homophobic but told Gazeta Wyborcza that although his election was a breakthrough for national politics, the residents of Warsaw are more open-minded.
He said: “I can’t compare myself to Harvey Milk, but I’m glad that I am the first openly gay candidate to be elected for a public office in Poland.”
Warsaw hosted Europride earlier in July but Poland has had an uneasy relationship with gay rights over the years.
The country is deeply Catholic and conservative and human rights groups say it has a poor record on gay equality.
Late president Lech Kaczynski, who died in a plane crash in April, had been accused of homophobia on a number of occasions.
Homosexuality is legal in Poland but couples cannot adopt children and there is no legal recognition of their relationships.