The DNA/RNA binding proteins TAR DNA-binding protein 43 (TDP-43) and fused-in-sarcoma (FUS) are genetically linked to amyotrophic lateral sclerosis and frontotemporal lobar dementia, while the inappropriate cytoplasmic accumulations of TDP-43 and FUS are observed in a growing number of late-onset pathologies including spinocerebellar ataxia 3, Alzheimer's and Huntington's diseases (HD). To investigate if TDP-43 and FUS contribute to neurodegenerative phenotypes, we turned to a genetically accessible Caenorhabditis elegans model of polyglutamine toxicity. In C. elegans, we observe that genetic loss-of-function mutations for nematode orthologs of TDP-43 or FUS reduced behavioral defects and neurodegeneration caused by huntingtin exon-1 with expanded polyglutamines. Furthermore, using striatal cells from huntingtin knock-in mice we observed that small interfering ribonucleic acid (siRNA) against TDP-43 or FUS reduced cell death caused by mutant huntingtin. Moreover, we found that TDP-43 and the survival factor progranulin (PGRN) genetically interact to regulate polyglutamine toxicity in C. elegans and mammalian cells. Altogether our data point towards a conserved function for TDP-43 and FUS in promoting polyglutamine toxicity and that delivery of PGRN may have therapeutic benefits.