Hepatic stellate cell (HSC) activation induced by transforming growth factor β (TGF-β1) plays a pivotal role in the fibrogenesis. The complex downstream mediators of TGF-β1 are largely unknown. Here, proteomics analysis and biological validation demonstrated that methionine adenosyltransferase 2A (MAT2A) was significantly upregulated in a CCl4-induced fibrosis mice model and a small molecule NPLC0393, known to block TGF-β1/Smad3 signaling, inhibited its upregulation. In HSC cells, TGF-β1 induced elevation of MAT2A and MAT2β expression as well as reduction of S-adenosylmethionine (SAM) content, which further promoted HSC activation. Functionally, in vivo and in vitro knockdown of MAT2A alleviated CCl4- and TGF-β1-induced HSC activation, whereas in vivo overexpression of MAT2A facilitated hepatic fibrosis and abolished therapeutic effect of NPLC0393. TGF-β1 induced p65 phosphorylation and NF-κB activation, thereby promoted the transcription of MAT2A and its protein expression. In addition, overexpression of p65 abrogated NPLC0393 mediated inhibition of HSC activation. This study identified a novel pathway TGF-β1/p65/MAT2A that was involved in the regulation of intracellular SAM contents and liver fibrogenesis, suggesting that this pathway is a potential therapeutic target for hepatic fibrosis.