This study investigates the long-term emergence of settlement scaling in Ancient Southwest Asia by analysing house-size data from 1,852 buildings across 80 archaeological sites dating from the Late Epipalaeolithic to the Iron Age (c. 13,100–580 BCE). Using domestic architecture as a proxy for household productivity, we provide the first fully diachronic test of settlement scaling theory in the region where urbanisation first developed. Mixed-effects models reveal that scaling relationships were absent in the Neolithic, ambiguous in the Chalcolithic, and only fully emerged in the Bronze Age, where sub-linear exponents align with theoretical predictions for intensive socioeconomic outputs. These patterns persist into the Iron Age, indicating that strongly mixing interaction networks—central to settlement scaling theory—became structurally embedded only with the rise of urban complexity. Across periods, baseline house size more than doubles, suggesting long-term technological or organisational improvements independent of agglomeration effects. We also examine how scaling relates to economic inequality using Gini coefficients of residential size distributions. Inequality correlates with settlement size only in politically complex systems and primarily at major centres, indicating that institutional structures—not agglomeration-driven productivity—govern the allocation of returns. Residuals from scaling models do not predict inequality, demonstrating that productivity gains and their distribution operate through independent channels. Finally, we derive period-specific estimates of population density from the intercepts of area-population scaling relationships. These results document a marked decline in residential density from the Chalcolithic to the Bronze Age, followed by partial recovery in the Iron Age, aligning with independent reconstructions from sites such as Tell Brak. Overall, the study shows that scaling behaviours emerged only with sustained urban integration, and that inequality in early cities was shaped more by political institutions than by the geometric constraints of urban interaction.