Iris took home five Best Awards and seven merits, as well as the Agency of the Year accolade, beating off competition from Initials Marketing, Elvis, Livity and Saatchi & Saatchi X.
BD Network also had a very successful night, winning four Best Awards and four merits, while Best Breakthrough Agency of the Year was won by Forever Beta.
The 'Final Verse' campaign by specialist youth marketing agency Livity for the NSPCC's ChildLine service, won the Best Social Media Campaign, Best Consumer Campaign and Best of the Best awards.
Guardian readers voted for the Best Consumer Campaign, while the client judges awarded the Best of the Best award.
The plaudits for Livity marked the first time a social media campaign has won three of the top awards.
The awards, now in their 22nd year, were judged by both clients and agency creative directors, with Iris founder and worldwide chief executive Ian Milner introducing the awards in his role as chairman of the MAA.
Simon Tilden, Diageo's global category director of advertising and ideation, was chairman of the judges, while the creative judging panel was chaired by Alistair Ross, DraftFCB's head of ideas.
Tilden said: "We especially liked work in the digital categories, where we saw powerful innovative campaigns exploiting social media channels."
Millner said: "It's great to be Agency of the Year and Most Awarded Agency. We've had one hell of a ride over the last few years, and that helps make these awards feel so special."
Follow Matthew Chapman at @mattchapmanUK