Migration independently evolved numerous times in animals, with a myriad of ecological and evolutionary implications. In fishes, perhaps the most extreme form of migration is diadromy, the migration between marine and freshwater environments. A key and longstanding question is how does diadromy influence lineage diversification rates? Many diadromous species travel long distances during migration, have large geographic ranges, and use isolated freshwater habitats, which may increase the likelihood of speciation. Alternatively, diadromy may reduce lineage diversification rates if migration facilitates gene flow, homogenizing populations and stymieing speciation. Clupeiformes (herrings, sardines, shads and anchovies) is a model clade for testing hypotheses about the evolution of diadromy because it includes an exceptionally high proportion of diadromous species and several independent evolutionary origins of diadromy. However, relationships among major clupeiform lineages remain unresolved with sparse (<50%) sampling of diadromous species, limiting the resolution of phylogenetically-informed statistical analyses. We assembled a phylogenomic dataset and used multi-species coalescent and concatenation approaches to generate the most comprehensive, highly-resolved clupeiform phylogeny to date, clarifying relationships among major clades of Clupeiformes, revealing taxa requiring revision, and identifying recalcitrant relationships needing further examination. Using this phylogeny as the evolutionary framework for downstream comparative analyses, we tested the hypothesis that diadromous lineages diversified faster than lineages restricted to either marine or freshwater habitats. We found that transitions to diadromy were more common than transitions from diadromy to non-diadromy. The largest lineage diversification rate increase in clupeiforms is associated with a transition to diadromy, but we uncovered little statistical support for categorically faster lineage diversification rates in diadromous versus non-diadromous fishes. We propose that diadromy may increase the potential for accelerated lineage diversification, particularly in species that migrate long distances, but this potential may only be realized in certain biogeographic contexts.