Pathological forms of TAR-binding protein 43 (TDP-43) are present in frontotemporal dementia (FTD), Alzheimer’s disease, and almost all amyotrophic lateral sclerosis (ALS) cases. Hence, identifying mechanisms that induce TDP-43 pathology are central to neurodegeneration and developing new therapeutic strategies. Actin has important roles in neurons, and it exists in dynamic equilibrium between monomeric G-actin and polymeric F-actin. Cofilin is an important actin-binding protein regulating actin dynamics. Its activity is controlled by phosphorylation (Ser3), which renders it inactive.Here, we demonstrate that dysregulated actin dynamics induces TDP-43 pathology in sporadic ALS. Actin dynamics was dysregulated in sporadic ALS, rNLS8 mice and neuronal cells expressing cytoplasmic TDP-43. Increased F-actin and enhanced cofilin phosphorylation were detected in spinal cord motor neurons of sporadic patients and mice with TDP-43 pathology. Pharmacological actin polymerization using Jasplakinolide induced TDP-43 pathology and recruitment to stress granules.  TDP-43 interacted with actin and co-localised with cofilin in motor neurons.  Cofilin peptides containing Ser3 rescued TDP-43 pathology, implying that cofilin phosphorylation is a therapeutic target for neurodegeneration.This is the first study to demonstrate that dysregulation of actin dynamics and the LIMK1/2-cofilin pathway are associated with TDP-43 pathology in ALS/MND. Moreover, we confirmed these defects are present in sporadic ALS/MND patients, thus are applicable to most cases. This study therefore identifies novel therapeutic targets for TDP-43 pathology in ALS/MND.