During the 2015 “summer of welcome”, the mass arrival of refugees to Germany triggered widely publicised acts of pro-refugee solidarity among citizens. To date, scholarship has largely focused on hostility towards immigrants—including refugees-, and few studies shed light on the determinants of acceptance, so that refugee solidarity remains poorly understood. In this paper, we hypothesise that pro-refugee engagement does not just reflect humanitarian concerns, but also a more general acceptance of socio-cultural diversity in German society. Relying on unique survey data gathered in 2019–2020, we show that a majority of urban Germans indeed engaged in some form of support. We employ latent class analysis to capture the spectrum of diversity attitudes within the urban population. A series of regression models show that diversity attitudes are powerful predictors of pro-refugee engagement. Overall, our study helps advancing immigration scholarship by demonstrating that widespread support for refugees is strongly associated with more general diversity assent.