Biodiversity varies across the world and is influenced by multiple factors, such as environmental stability and past historical events (e.g., Panama Isthmus). At same time, organisms with unique life-histories (e.g., parasites) are subject to unique selection pressures that structure their diversity patterns. Parasites represent one the most successful life-strategies, impacting directly and indirectly the ecosystem by cascading effects on host fitness and survival. Here, I focused on a highly diverse, prevalent, and cosmopolitan group of parasites (avian haemosporidians) to investigate the main drivers of regional parasite diversity on a global scale. To do so, I compiled data from four global datasets on (i) avian haemosporidian (malaria and malaria-like) parasites, (ii) bird species richness, (iii) avian functional traits, and (iv) climate data. Then, using generalized mixed models, I evaluated potential drivers of haemosporidian diversity. I found that haemosporidian diversity is driven by both host regional diversity and functional traits, and by environmental conditions. In other words, parasite diversity increased with increasing host richness and higher numbers of resident and territorial birds. Further, greater temperature seasonality was also positively correlated with parasite diversity. Hence, regions harboring the greatest resident/territorial avian diversity (e.g., neotropics) and/or higher temperature seasonality (e.g., North America) generally harbor the highest diversity of haemosporidian parasites. Overall, I demonstrated that haemosporidian parasite diversity is intrinsically associated with their hosts’ diversity and functional traits.