Trai has worked extensively with BirdLife since its early years in Vietnam. Prior to joining BirdLife in 2002, Trai has worked for more than 20 years as a researcher and planner for the Forest Inventory and Planning Institute (FIPI), a leading institute in forestry under the Ministry of Agriculture and Rural Development.

Trai was formerly the senior project officer on the collaborative BirdLife–FIPI project “Expanding the Protected Areas Network in Vietnam for the 21st Century”. This European Union-funded project provided support for the implementation of the Government of Vietnam's policy commitment to expand the national network of protected areas. Prior to this, he was project officer on the project entitled “The Conservation of Biodiversity in the Annamese Lowlands and the Da Lat Plateau, Vietnam”, which was also funded by the European Union.

Trai's work has concentrated on biodiversity surveys, monitoring the wildlife resources of Vietnam, and protected areas planning. He is now recognised as one of Vietnam's leading field ecologists. He has discovered an undescribed taxon of muntjac and re-discovered Roosevelt's Muntjac. He was also involved in the discovery of new species of birds in Central Vietnam: Black-crowned Barwing, Golden-winged Laughingthrush, and Chestnut-eared Laughingthrush. Trai recently co-authored Vietnam's first Vietnamese-language bird field guide Chim Viet Nam. He has published extensively on the fauna of Vietnam. He also has extensive experience of production of feasibility studies, investment plans and management plans for the establishment and efficient operation of protected areas in Vietnam.

Trai’s extensive technical experience combined with conservation project planning and management experience has been an asset for BirdLife Vietnam Programme,  in its move from extensive biodiversity research and surveys, to more site action projects.