Cytoplasmic transactive response DNA-binding protein 43 (TDP43) mislocalization and aggregation are pathological hallmarks of amyotrophic lateral sclerosis (ALS). However, the initial cellular insults that lead to TDP43 mislocalization remain unclear. In this study, we demonstrate that nemo-like kinase (NLK) - a proline-directed serine-threonine kinase - promotes the mislocalization of TDP43 and other RNA-binding proteins by disrupting nuclear import. NLK levels were selectively elevated in neurons exhibiting TDP43 mislocalization in tissues from patients with ALS, and genetic reduction of NLK reduced toxicity in human neuron models of ALS. Our findings suggest that NLK is a promising therapeutic target for neurodegenerative diseases.