Jon Moseley, Rowan's managing director, said the rebrand will cover everything from letterheads to outdoor signage and will include a redesign of Warwick's website.
"They want to raise their profile in the global marketplace and we are looking at a marketing campaign through specialist chemical publications around the world," he said.
He said the three-year deal was an important contract for Rowan which would also be handling the Mostyn firm's PR.
Warwick International was bought by its management team two years ago in a £129m deal backed by London-based Close Brothers Private Equity and a banking syndicate led by The Royal Bank of Scotland.
The firm is a global leader in the manufacture of oxygen-based bleaching systems for the detergents and biocides industries. Its core product is the key ingredient in many of the world's leading detergent products, including washing powder and dishwasher detergents. Established as a start-up operation at Mostyn in 1979, the firm is a major exporter.
Rowan says the Warwick account is one of a number of recent, new business wins. Mr Moseley, who set up Rowan a quarter of a century ago, said: "It is great to see increased optimism across so many industries and firms willing to make sensible investments to build their businesses and brands.
"Our specialism is in opening doors and developing sales by using all media including powerful direct and digital marketing."
Rowan has won five national Direct Marketing Awards - awards which were judged on the results its clients had achieved through using its services.
Based at Tattenhall, near Chester, the firm operates across all sectors and has major national clients including one of the UK's top five high street banking groups.
The agency, a recognised leader in direct marketing, also numbers organisations as diverse as motor groups and health companies amongst its clients.