Gracillariidae is the most taxonomically diverse cosmopolitan leaf-mining moth family, consisting of nearly 2000 named species in 105 described genera, classified into eight extant subfamilies. The majority of gracillariid species are internal plant feeders as larvae, creating mines and galls in plant tissue. Despite their diversity and ecological adaptations, their phylogenetic relationships, especially at the subfamily level, remain largely uncertain. Genomic data (83 taxa and 589 loci) were integrated with Sanger data (130 taxa and 22 loci), to reconstruct a phylogeny of Gracillariidae. Based on analyses of both data sets combined and analyzed separately, the monophyly of Gracillariidae and all its subfamilies, and the monophyly of the clade ‘LAMPO’ (subfamilies: Lithocolletinae, Acrocercopinae, Marmarinae, Phyllocnistinae, and Oecophyllembiinae) and relationships of its subclade ‘AMO’ (subfamilies: Acrocercopinae, Marmarinae, and Oecophyllembiinae) were strongly supported. A sister group relationship of Ornixolinae to the remainder of the family, and a monophyletic leaf roller lineage (Callicercops Vári + Parornichinae) + Gracillariinae, as sister to the ‘LAMPO’ clade were supported by the best hypotheses. Based on these results, a new subfamily, Callicercopinae Li, Ohshima et Kawahara, is established to accommodate the enigmatic genus Callicercops. Dating analyses indicate a mid-Cretaceous (105.3 Ma) origin of the family, followed by a rapid diversification into the nine subfamilies predating the K-Pg extinction. We hypothesize that advanced larval behaviours, such as making keeled or tentiform blotch mines, rolling leaves, and making galls, accelerated the diversification of Gracillariidae by avoiding larval parasitoids.