The environmental price of fashion has been heavily scrutinised in recent years. Slow fashion, with its emphasis on quality, design, sustainability, ethicality and local craft heritage, represents an alternative to the harmful environmental and social impact of fast fashion. Equally important, some initial evidence from qualitative research suggests that slow fashion could enhance consumers’ well-being. The present study aims to quantitatively evaluate the relationships that fast and slow fashion may have with different domains of well-being, utilising Seligmen’s influential PERMA model from positive psychology. In addition, it explores characteristics from slow fashion that may enhance garment lifetimes. An online questionnaire successfully surveyed 763 urban Chinese consumers. Results showed that consumption of slow fashion, in particular ‘customised/bespoke clothing’ that allows consumers to be actively involved in the creation process, positively predicted three well-being domains—engagement, meaning and achievement. Fast fashion, on the other hand, negatively predicted these domains. Classic/timeless design, ease of maintenance and ease of matching with other clothes emerged as the three most important characteristics that may encourage consumers’ long-term use of fashion items. Implications of the findings are discussed in the context of promoting slow fashion to enhance sustainability.