The phytohormone abscisic acid (ABA) is important for growth, development and stress responses in plants. Recent research has identified ABA receptors and signalling components that regulate seed germination and stomatal closure. However, proteins that regulate ABA signalling remain poorly understood. Here we use a forward-genetic screen to identify rbm25-1 and rbm25-2, two Arabidopsis mutants with increased sensitivity to growth inhibition by ABA. Using RNA-seq, we found that RBM25 controls the splicing of many pre-mRNAs. The protein phosphatase 2C HAB1, a critical component in ABA signalling, shows a dramatic defect in pre-mRNA splicing in rbm25 mutants. Ectopic expression of a HAB1 complementary DNA derived from wild-type mRNAs partially suppresses the rbm25-2 mutant phenotype. We suggest that RNA splicing is of particular importance for plant response to ABA and that the splicing factor RBM25 has a critical role in this response.