Gathy was born in Brussels, Belgium, in 1955 and grew up in Liege from the age of five. After he graduated 1978, he got a job at the University of Liege working with a collaborative of architects.

He was sent to Indonesia on a project and fell in love with Asia. In 1983, he moved to Hong Kong where he set up his own architectural firm, Denniston Architects. He then moved to Malaysia, and has been based in Kuala Lampur ever since.

He is the principal designer and public face of Denniston International Architects, Interior Designers and Planners, where his clients include Amanresorts, One&Only, Park Hyatt, Mandarin Oriental, Cheval Blanc, Armani, St. Regis, Raffles, Setai, Chedi, Jumeirah, Banyan Tree, Shangri-La, and more.

Some of the completed projects for which he is responsible include the immensely successful One&Only Reethi Rah in the Maldives, the Setai Miami, the Chedi Muscat in Oman, the St. Regis Lhasa in Tibet, and the Fuchun Resort in China.

Gathy has received personal and project awards, participated as a jury member for various project awards, and has been invited as an official guest speaker at international forums and to aspiring architects.