The growing literature on the influence of state architectures on women’s politics is a dynamic and emerging field of research. However, to date, this literature has not fully evaluated the relationship between state architectures and women’s political representation. When work in this area has addressed women’s descriptive representation, it has often underplayed or ignored party political factors. Meanwhile, when we turn to the literature on party politics, we find another paradox: research on gender and party politics neglects the multi-level dynamics of the political setting, while the growing body of work on territorial party politics neglects issues of women and gender. This paper seeks to assess the impact of state architectures on strategies to increase women’s numerical representation. To do so, we undertake a small-n comparison of candidate selection reform over time in two decentralized European countries: the UK and Spain. The article has three main goals. First, we aim to disentangle how the relationship between state architectures and women’s representation is mediated by party organization, particularly by the multi-level party dynamics which arise from the territorial structure of the state. Second, we will analyzethe ways in which party feminists have played the ‘two-level game’, that is how have women transferred their activism across institutional arenas, in pushing for candidate selection reform at both the party and institutional level. And, finally, we seek to assess under what circumstances can positive gender outcomes – in this case, numerical increases in women’s political representation – be achieved