The Dentsu Aegis Network agency will handle Monster’s advertising across 23 European countries, developing new work across digital, radio, social, print and TV under the "Find Better" tagline.
The BBDO network was the incumbent on the account, having held it since 2007. Leo Burnett had previously handled the brand's advertising on a project basis.
KBS was named as the brand’s lead global agency in January.
OMD handles Monster's media planning and buying, which in the UK is run out of Manning Gottlieb OMD. The Omnicom network picked up the business in 2009.
Andrew Warner, the European marketing lead at Monster, said: "After an exhausting and thorough process Mcgarrybowen impressed us with their creative and strategic thinking.
"It’s great to be working with an agency partner that shares our ambition for the brand."