It is the first agency to work with LINE since it launched in 2011, offering a range of free call and messaging apps.
Ketchum's brief is to raise awareness of the new range of LINE gaming apps, its movie maker app Snapmovie and a free calling service and help to secure UK media coverage of LINE’s annual conference.
Ketchum will report to LINE’s European PR manager Federica Calcaterra.
The total number of global downloads of LINE Messenger and LINE family apps topped one billion in June this year.
Calcaterra said: "LINE is excited to continue growing in Europe and Ketchum is the perfect partner to help raise our profile with consumers in the UK and Spain. We recently celebrated our third anniversary and hope to continue providing users with a fantastic choice of mobile apps and services. Ketchum’s global network means it has the necessary expertise and experience to help us stay relevant in the European market."
David Vindel, managing director, European technology at Ketchum, added: "LINE Corporation has a brilliant range of mobile apps that is already loved by a global audience. We look forward to helping LINE grow its market share in Europe and continuing its remarkable success."