Notomicrinae (Coleoptera: Noteridae) is a subfamily of minute and ecologically diverse aquatic beetles distributed across the Southeast Asia, Oceania, and the Americas. We investigate the evolution of Notomicrinae and construct the first species-level phylogeny within Noteridae using five nuclear and mitochondrial gene fragments. We focus on the genus Notomicrus Sharp (Coleoptera: Noteridae), sampling 13 of the 17 known Notomicrus species and an additional 11 putative undescribed species. We also include Phreatodytes haibaraensis Uéno (Coleoptera: Noteridae). Datasets are analyzed in Maximum Likelihood and Bayesian frameworks. With these, we 1) estimate divergence times among notomicrine taxa and reconstruct the biogeographical history of the group, particularly testing the hypothesis of Gondwanan vicariance between Old World and New World Notomicrus; 2) additionally, we assess ecological plasticity within Notomicrinae in the context of the phylogeny; and 3) finally, we test the monophyly of tentative species groups within Notomicrus and place putative new taxa. We recover a monophyletic Notomicrinae, with Phreatodytes sister to Notomicrus. We estimate the crown age of Notomicrinae to be ca. 110 Mya. The crown age of Notomicrus is recovered as ca. 75 Mya, there diverging into reciprocally monophyletic Old and New World clades, suggesting Gondwanan vicariance. Our phylogenetic estimate indicates a strong degree of ecological plasticity within Notomicrinae, with habitat switching occurring in recently diverging taxa. Finally, we recover five main species groups in Notomicrus, one Old World, Four New World, with tentative affirmation of the placement of undescribed species.