A Taiwan origin for the expansion of the Austronesian languages and their speakers is well supported by linguistic and archaeological evidence. However, human genetic evidence is more controversial. Until now, there had been no ancient skeletal evidence of a potential Austronesian-speaking ancestor prior to the Taiwan Neolithic ~6,000 years ago, and genetic studies have largely ignored the role of genetic diversity within Taiwan as well as the origins of Formosans. We address these issues via analysis of a complete mitochondrial DNA genome sequence of an ~8,000-year-old skeleton from Liang Island (located between China and Taiwan) and 550 mtDNA genome sequences from 8 aboriginal (highland) Formosan and 4 other Taiwanese groups. We show that the Liangdao Man mtDNA sequence is closest to Formosans, provides a link to southern China, and has the most ancestral haplogroup E sequence found among extant Austronesian speakers. Bayesian phylogenetic analysis allows us to reconstruct a history of early Austronesians arriving in Taiwan in the north ~6,000 years ago, spreading rapidly to the south, and leaving Taiwan ~4,000 years ago to spread throughout Island Southeast Asia, Madagascar, and Oceania.