Species richness varies among clades, yet the drivers of diversification creating this variation remain poorly understood. While abiotic factors likely drive some of the variation in species richness, ecological interactions may also contribute. Here, we examine one class of potential contributors to species richness variation that is particularly poorly understood: mutualistic interactions. We aim to elucidate large-scale patterns of diversification mediated by mutualistic interactions using a spatially-explicit population-based model. We focus on mutualistic Müllerian mimicry between conspicuous toxic prey species, where convergence in colour patterns emerges from predators' learning process. To investigate the effects of Müllerian mimicry on species diversification, we assume that some speciation events stem from shifts in ecological niches, and can also be associated with shift in mimetic colour pattern. Through the emergence of spatial mosaics of mimetic colour patterns, Müllerian mimicry constrains the geographical distribution of species and allows different species with similar ecological niches to exist simultaneously in different regions. Müllerian mimicry and the resulting spatial segregation of mimetic colour patterns thus generate more balanced phylogenetic trees and increase overall species diversity. Our study sheds light on complex effects of Müllerian mimicry on ecological, spatial and phylogenetic diversification.