Severe fever with thrombocytopenia syndrome phlebovirus (SFTSV), listed in the World Health Organization Prioritized Pathogens, is an emerging phlebovirus with a high fatality^{, , –}. Owing to the lack of therapies and vaccines^,, there is a pressing need to understand SFTSV pathogenesis. SFSTV non-structural protein (NSs) has been shown to block type I interferon induction^{, , , –} and facilitate disease progression^,. Here, we report that SFTSV-NSs targets the tumour progression locus 2 (TPL2)–A20-binding inhibitor of NF-κB activation 2 (ABIN2)–p105 complex to induce the expression of interleukin-10 (IL-10) for viral pathogenesis. Using a combination of reverse genetics, a TPL2 kinase inhibitor and Tpl2^−/− mice showed that NSs interacted with ABIN2 and promoted TPL2 complex formation and signalling activity, resulting in the marked upregulation of Il10 expression. Whereas SFTSV infection of wild-type mice led to rapid weight loss and death, Tpl2^−/− mice or Il10^−/− mice survived an infection. Furthermore, SFTSV-NSs P₁₀₂A and SFTSV-NSs K₂₁₁R that lost the ability to induce TPL2 signalling and IL-10 production showed drastically reduced pathogenesis. Remarkably, the exogenous administration of recombinant IL-10 effectively rescued the attenuated pathogenic activity of SFTSV-NSs P₁₀₂A, resulting in a lethal infection. Our study demonstrates that SFTSV-NSs targets the TPL2 signalling pathway to induce immune-suppressive IL-10 cytokine production as a means to dampen the host defence and promote viral pathogenesis.