The sport was widely tipped to win ahead of the ceremony on Saturday. In the end, "grrr" was chosen by 17 out of the 22 jurors as the Grand Prix winner.
"Grrr" beat the next closest contender, the TBWA\Chiat\Day dream-like Adidas spot "hello tomorrow", which was directed by Spike Jonze.
John Hunt, TBWA\Worldwide creative director and jury chairman, said: "I asked the jury to write secret ballots for their first and second favourites for the award.
"For second, the Adidas spot 'hello tomorrow' and a few others were also mentioned. But there was no discussion about the Grand Prix."
"Grrr" saw Wieden & Kennedy London follow up its acclaimed "cog" spot for Honda, which missed out on the Grand Prix in 2003, with a lushly animated, catchily soundtracked film that, Hunt said, "entertains you as it sells you" Honda's diesel technology.
UK agencies won three Gold Lions, behind US agencies who took five, and ahead of France and Thailand with two.
Lowe London took one of the Golds for its recent "stunt city" ad for Sure/Rexona, while Saatchi & Saatchi also won for its creepy "ventroloquist" for the NSPCC.
TBWA\London's series of three films for PlayStation2, showing a surreal PlayStation world inhabited by tribes where athletes are set upon by ventriloquists, was awarded a Gold.
With TBWA\Paris taking the agency of the year award, the network had a successful festival. DDB London came second in agency of the year and DDB Paris came third.
In the new integrated category, four Titanium Lions were given out, including one for the extension of "grrr"'s 'Hate Something Change Something' theme across radio, TV, cinema, press, interactive TV and the internet. The campaign generated an increase of 43% in the number of people visiting Honda's website and an increase of 62% in spontaneous brand awareness.
The other Titanium Lions winners were Host Australia for "5 cent" for Virgin Mobile Australia; Crispin Porter & Bogusky Miami for "counterfeit" for Mini Cooper; and Fuel Europe for "life on board project" for Volvo.
The inaugural Radio Lions were dominated by the US, with DDB Chicago taking the Grand Prix for the Bud Light "Real Men of Genius" campaign, featuring multiple spots in which Budweiser salutes unsung heroes such as Mr Cargo Pants Designer and Mr Pro Sport Heckler Guy. The few UK agencies shortlisted failed to win any Lions.
If you have an opinion on this or any other issue raised on Brand Republic, join the debate in the .