The appointment follows a competitive pitch that began in November last year and was believed to have involved four other agencies.
Kayak spent £2 million in the UK last year, according to Nielsen. However, this is expected to be supplemented by significant digital spend.
The review also includes media activity in France, Italy, Spain and Poland, with spend expected to be in the region of £20 million over the coming year.
Belinda Rowe, a managing partner at ZenithOptimedia Worldwide, said: "Kayak’s global websites and mobile apps are experiencing phenomenal growth."
Kayak’s media review follows its acquisition by the US company Priceline Group in November last year in a deal that valued the business at $1.8 billion.