Global mobility of scientists is an important modern phenomenon with economic and political implications. As scientists become ever more footloose it is important to identify general patterns and regularities at a global scale. At the same time cities, and especially global cities, have become important loci of economic and scientific activity. Limiting research to international migration, would disregard the importance of local innovation systems. The analysis of the mobility and brain circulation patterns at global scale remains challenging, due to difficulties in obtaining individual level mobility data. In this work we propose a methodology to trace intercity and international mobility through bibliographic records. We reconstruct the intercity and international mobility network of 3.7 Million Life Scientists moving between 9,745 cities. We present several features of the extracted network, offer evidence that the international innovation system is marked by national borders and linguistic similarity and show that international mobility largely contributes to the scientific output of national research systems. Moreover we find evidence to suggest that global cities attract highly productive scientist early in their careers.