The fashion retailer retained its incumbent UK and Ireland agency after a final shootout against Aegis' Vizeum and Publicis agency ZenithOptimedia.
Andy Jones, the UM chief executive, said: "We are incredibly proud of the work we've done in collaboration with H&M and look forward to building upon that going forward. H&M is a flagship client for UM and we truly value their business."
The review followed a separate review late last year for H&M's outdoor media account which moved from Interpublic's IPM specialist and into WPP's Kinetic.
UM has handled the media planning and buying business for the Swedish retailer since September 2001 and last defended the contract in 2004.
H&M also launched its first online shop last week. The retail giant has announced a new designer collaboration with Lanvin, the luxury French fashion label, which will create a range to hit shops in December.
H&M launched a festival range this summer from which 25% of sales were donated to youth HIV/Aids awareness projects. It is part of the store's Fashion Against Aids campaign, now in its third year, which has raised over £2.7m for charity.