The current study was designed to evaluate the anti-oxidant and anti-arthritic potential of a traditionally used herb, Monotheca buxifolia. The M. buxifolia methanolic extract (MBME) was prepared from the aerial parts of the plant followed by chemical characterization with GC-MS. The anti-oxidant potential of the MBME was demonstrated by DPPH scavenging activity. The effects of MBME on protein denaturation and membrane stabilization were determined by inhibition of egg albumin denaturation and RBC membrane stabilization assays, respectively. The in vivo anti-arthritic potential of the MBME at 50, 100, and 150 mg/kg/day was evaluated in Complete Freund's Adjuvant-induced polyarthritis in Wistar rats treated for 21 days. Phytochemicals, such as linolenic acid methyl ester, n-hexadecanoic acid, vitamin E, α-amyrin, and β-amyrin were detected in the GC-MS analysis. The plant extract exhibited a 55.20 ± 0.69% scavenging of free radicals at 100 µg/ml concentration. It significantly (p < 0.05) stabilized human RBC membrane (65.06 ± 0.22%) and inhibited protein denaturation (70.53 ± 0.34%) at 100 mg/ml concentration. The diclofenac sodium (DS) and MBME at 150,100, and 50 mg/kg reduced the paw edema, restored the body weight, and altered blood parameters including CRP. The MBME significantly reduced the MDA and increased the SOD, CAT, and GSH levels in liver tissue homogenate in treated rats. The serum concentration of TNF-α and PGE2 was remarkably (p < 0.01-< 0.0001) restored by the DS and MBME dose dependently. The histopathological study showed that MBME 150 mg/kg commendably restored the ankle joint inflammation, bone erosion, and cartilage damage in polyarthritic rats. It was concluded that the anti-oxidant, anti-inflammatory and anti-arthritic effects of MBME might be attributed to phenols, flavonoids, triterpenoids, vitamin E, phytol, and other fatty acids. This study showed the anti-arthritic potential of Monotheca buxifolia and thus validates its traditional claim.