This study examines the contribution of Chinese diaspora researchers – those born in China but working outside the country – to China's catching up in global science to become a world leader in research publications and citations. Using a novel name-based way to identify Chinese diaspora authors of scientific papers, we show that these researchers produce a large proportion of global scientific papers of high quality, gaining about twice as many citations as other papers of the same vintage. Our analysis also shows that diaspora researchers are a critical node in the co-authorship and citation networks that connect scientific discovery in China with the rest of the world. In co-authorship, diaspora researchers are over-represented on international collaborations with China-addressed authors. In citations, a paper with a diaspora author is more likely to cite China-addressed papers than a non-China addressed paper without a diaspora author; and, commensurately, China-addressed papers are more likely to cite a non-China addressed paper with a diaspora author than a non-China paper without a diaspora author. Through those pathways, diaspora research contributed to China’s 2000-2015 catch-up in science and to global science writ large, consistent with ethnic network models of knowledge transfer, and contrary to brain drain fears that the emigration of researchers harms the source country.