The terminal migration of Homo erectus in Southeast Asia during Early Pleistocene is cardinal to our comprehension of the evolution of the genus Homo. However, the limited consideration of the rapidly changing physical environment, together with controversial ages of hominin bearing sites, make it challenging to secure the necessary robust timeline. Here, we reappraise the first appearance datum of Javanese H. erectus by adding to a compilation of earlier estimates the most reliable age constraints based on cosmogenic nuclides 10 Be and 26 Al produced in situ. We find that H. erectus reached Java and dwelled at Sangiran, Java, at least ⇠1.4 Ma ago and more probably around 1.8 Ma. Using this age as a baseline, we develop a probabilistic approach to reconstruct their dispersal routes, coupling ecological movement simulations to landscape evolution models. We demonstrate that the hospitable terra firma conditions of Sundaland facilitated the prior dispersal of hominins to the edge of Java, where they conversely could not settle until the Javanese archipelago emerged from the sea and connected to Sundaland. We estimate a characteristic dispersal time of H. erectus across Sundaland of a few tens to hundreds kyrs, indicating that changes in their physical environment, whether climatic or physiographic, cannot be ignored. Our comprehensive reconstruction method to unravel the peopling timeline of SE Asia provides a novel framework to evaluate the evolution of early humans.