Theories of post-nationalism are concerned with deconstructing the relationship between citizenship and national identity. While literature in this field has tended towards macroinstitutionalist analysis, recent research has re-articulated post-nationalism as micro-level practice. This article builds on this development by attending to the 'affective conditions' of such micropolitical practices. The article draws on research into protests in Brisbane in February 2016 to prevent 'Asha', a child seeking asylum, from being returned to offshore detention. The analysis of this case demonstrates that affect performs a dual function in the practice of post-nationalism, to catalyse action in solidarity with the noncitizen informed primarily by the emotional resonance of a particular rendering of vulnerability, and in re-imagined solidarity with the co-citizen around a post-national community of feeling. Informed by this analysis, the article highlights the complex and fragile nature of a post-national solidarity dependent on intersecting, overlapping and at times problematic, affective conditions.