Scholarship on evidence-based policymaking (EBP) has long called for more a realistic understanding of how politicians use evidence, especially the ways that use of evidence is negotiated with political goals. This article offers a new perspective on this question by drawing from research on legislative organisations. It introduces a new framework for the study of evidence-based policy, developed by reviewing key insights from legislative studies and interpreting their relevance for the study of EBP. It then applies this framework in an interview-based case-study of the Parliament of Finland. Previous studies have identified timeliness and relevance as some of the key barriers to using evidence, and our data focus on how key actors in legislative organisations understand and manage timeliness. Our findings show that timeliness is dominated by short-term reactions to new bill proposals, but the window for timely evidence in the legislatures can vary from months to days. Our study identifies three strategies used in legislative organisations to overcome the problems of reactivity: programmatic work, specialisation and network building. Practices relating to these strategies are discussed across legislators, political parties and committees. Our findings suggest that it is important for research on EBP in a legislative context to go beyond the study of committees and individual legislators, to explore the role of political parties. This strategy allows researchers to discover the often non-linear and indirect ways that evidence can influence policy through political parties.