Anatomically Modern Humans (AMHs) dispersed rapidly through island southeast Asia (Sunda and Wallacea) and into Sahul (Australia, New Guinea and the Aru Islands), before 50,000 years ago. Multiple routes have been proposed for this dispersal and all involve at least one multi-day maritime voyage approaching 100 km. Here we use new regional-scale bathymetry data, palaeoenvironmental reconstruction, an assessment of vertical land movements and drift modeling to assess the potential for an initial entry into northwest Australia from southern Wallacea (Timor-Roti). From ∼70,000 until ∼10,000 years ago, a chain of habitable, resource-rich islands were emergent off the coast of northwest Australia (now mostly submerged). These were visible from high points close to the coast on Timor-Roti and as close as 87 km. Drift models suggest the probability of accidental arrival on these islands from Timor-Roti was low at any time. However, purposeful voyages in the summer monsoon season were very likely to be successful over 47 days. Genomic data suggests the colonizing population size was >72100 individuals, thereby indicating deliberate colonization. This is arguably the most dramatic early demonstration of the advanced cognitive abilities and technological capabilities of AMHs, but one that could leave little material imprint in the archaeological record beyond the evidence that colonization occurred.