Andrographis paniculata leaves have been widely used in traditional medicine due to their rich content of phenolic compounds. In this study, we evaluated the total phenolic and flavonoid content of Andrographis paniculata leaf extracts (ALE), as well as its antioxidant activities against DPPH, ABTS, and hydrogen peroxide radicals. Additionally, we conducted cell viability assays, RT-PCR, and western blot analysis to investigate the biochemical effects of ALE on UVB-induced HaCaT cells. Our results revealed that ALE exhibited a high concentration of polyphenols and flavonoids, which were associated with potent abiotic antioxidant properties. Furthermore, ALE treatment effectively abrogated the damage caused by UVB radiation on key molecules such as hyaluronan synthase 1, Aquaporin 3, and loricrin in HaCaT cells. ALE also demonstrated the ability to reduce the overactivation of mitogen-activated protein kinases (MAPKs) and the expression of pro-inflammatory cytokines, including interleukin-6 and interleukin-1β in UVB-induced HaCaT cells. Additionally, ALE positively influenced the peroxisome proliferator-activated receptor alpha in these cells. Overall, our findings highlight the antioxidant and anti-inflammatory effects of ALE, as well as its significant role in modulating skin barrier functions. These results contribute to the growing body of evidence supporting the therapeutic potential of ALE in skincare and dermatological applications.