The masked, horned quintet finished comfortably ahead of Russian hearthrob Dima Bilan and Bosnia-Herzegovina folk group Hari Mata Hari, smashing through a field of ballads and pop songs, mostly sung in English, with their fire-spewing, firework-exploding entry "Hard Rock Halleluja."
"How cool is this?" the band's bat-winged frontman "Mr Lordi" asked at the victory press conference for the annual song contest which attracts entries from Russia to Israel.
"We're a rock band, and we just won a pop song contest," he marvelled.
Thirty-five countries participated in this year's event, with 24 acts making it to Saturday's grand finale. Previous contest winners have included British '60s songstress Lulu, Swedish pop superstars Abba and Canadian diva Celine Dion who represented Switzerland.
The final tally saw Finland muster 292 points, ahead of Russia's 248 and Bosnia-Herzegovina's 229 in a voting system based on public phone and text voting in the participating nations.
The monster goth band's selection has embarrassed millions of Finns back home, but the band insisted on Sunday that had been voted to represent the country on the strength of a 42-percent majority vote.
The heavy metal entry enticed maximum votes from Finland's neighbors Denmark, Norway and Sweden, but also cast a spell on voters in Estonia, Iceland, Poland and Britain.
Mr Lordi hailed the result as "a victory for open-mindedness", expressing the hope that the pop-dominated contest will see a broader variety of music represented in future.
He also took the opportunity to insist that his band has nothing to do with Satanism, an accusation levelled by religious groups on the basis of some of their lyrics.
Nothing to do with Satan, band says
The video-clip for 'Hard Rock Hallelujah' shows the band storming into a school gymnasium, striking dead a group of cheerleaders and raising them again as zombies.
"We have nothing to do with Satan worship," Mr Lordi said. "This (act) is as serious as horror movies, this is entertainment."
In addition to the Eurovision title, the group also take home a prize limousine provided by Greek national broadcaster ERT.
The 51st edition of the festival hosted by Greece -- the winner of last year's contest -- featured an opening ceremony based on ancient Greek mythology of the deep seas, including floating waves, sirens, sea nymphs, dolphins and tritons.
Hosts Greece finished ninth in the contest, despite their rock ballad 'Everything' by Anna Vissi being counted among the top three pre-event favorites.
Vissi said she herself would have voted for Lordi, and Greece broke with its Eurovision tradition by awarding the monster-faced Finns the maximum 12 points, an honor usually reserved for neighbors Cyprus.
The German entry, country band Texas Lightning, came 15th overall in the contest with their song "No No Never."
By right of victory, Finland will now host the 2007 Eurovision contest.