Haloragaceae are a cosmopolitan plant family with its centre of diversity in Australia. Here, we investigate the historical biogeography of the family and the role of vicariance or dispersal in shaping its current distribution. DNA sequences from ITS, matK and the trnK 50 and trnK 30 introns were obtained for 102 species representing all 8 genera of Haloragaceae for use in Bayesian molecular dating. Molecular dating was conducted using two macrofossils as calibration points for the analyses. Biogeographic history was investigated using a Bayesian dispersal-vicariance analysis and a dispersal-extinction-cladogenesis model. The results suggest that the earliest diversification of the extant Haloragaceae occurred in Australia during the Eocene (37.3–56.3 Ma). Early diversification of the family in the Southern Hemisphere is inferred as resulting from vicariance events among Australia, South America and New Zealand. The results also indicate multiple out of Australia dispersal routes, primarily including (1) from Australia to Asia during the Miocene, with subsequent dispersal to Europe and North America; (2) from Australia to New Zealand, then to South America during the Miocene and Pliocene. Most of the inferred dispersal events occurred throughout the Miocene and later, and are biased towards the aquatic Haloragaceae lineages.