In an increasingly urbanized world, understanding the determinants of urban well-being will continue to grow in importance. Although the effects of different indicators of living conditions on well-being have been widely studied individually, little is known about their relative impact when examined jointly. In this study, we use a unique multi-source dataset that allows us to investigate the effect and relative importance of a variety of subjectively and objectively assessed aspects of urban living conditions on the subjective well-being (SWB) of German Foreign Service expatriates. The study captures living conditions in metropolises around the world at different stages of development, and assesses living conditions in a culturally comparably homogeneous set of participants, thus being potentially less confounded with cultural differences. Using linear regression and dominance analysis, we find that ‘quality of and access to nature’ (i.e., green space), ‘quality of housing’, and ‘quality of public goods’ (i.e., water, air, and sewage systems) have the strongest associations with SWB. Subjectively rated characteristics show stronger associations with SWB than externally assessed characteristics. Additionally, we examine whether the size of a city or the level of development of a country has an effect on SWB. Both living in a megacity (≥ 10 million inhabitants) and a lower development status have negative effects on SWB. However, these effects disappear when the various indicators of living conditions are controlled for. Our findings can inform organisations sending employees abroad as well as urban planners seeking to improve their policies and decision-making.