Karacsony called his victory "a lesson on democracy" after Fidesz-backed Istvan Tarlos conceded defeat, media reported.
With most ballots counted, Karacsony, 44, had the support of more than 50 per cent of voters in the capital, compared with just over 44 per cent for Tarlos, 71, mayor of Budapest since 2010.
Is Humour the Best Antidote to Tyranny?
British-American author Andrew Keen has been travelling the globe to investigate what he calls "the contemporary crisis of democracy" for his Keen On Democracy podcast series.
In this episode, he talks to Michael Zantovksy, a Czech diplomat, writer and human rights activist, on how to fight authoritarianism with humour.
President Klaus Iohannis on Friday, August 23, the Day of Remembrance for Victims of Fascism and Communism, released a message in which he underscores that this day compels us to reiterate "firm" condemnation of both ideologies, in all their forms, and to remember the innocent victims of those regimes.