Stellaria media (L.) Vill. is widely distributed throughout the world and is traditionally used to treat inflammatory, respiratory, cardiovascular, and gastrointestinal diseases. This study was designed to phytochemically characterize and investigate the anti-ulcer activity of methanol extract of S. media (SME) in piroxicam (PRX)-induced gastric ulcer in rats. The plant extract was subjected to qualitative as well as quantitative analysis (HPLC and FT-IR) to elucidate the phytochemical composition. In vitro, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay was done to determine the antioxidant capacity. In 14 days of animal study, PRX (30 mg/kg, i.g.) was co-administered with omeprazole (OMP; 20 mg/kg, i.g.) as a standard gastroprotective drug and SME at 150, 300, and 450 mg/kg, i.g., respectively. The gastric pH, acid volume, acidity, ulcer score, hematological parameters, and serum levels of oxidants/antioxidants were determined along with histopathological studies of gastric tissue. Phytochemical analysis showed the presence of considerable phenolic and flavonoid contents which was corroborated with a significant DPPH radical scavenging (IC50: 27.94 µg/mL) activity of extract. Administration of SME at 150, 300, and 450 mg/kg exhibited a dose-dependent gastroprotective effect evidenced by an increase in gastric pH and acidity but a decrease in gastric acid volume, gastric ulcer score, and ulcer index. Treatment with SME normalized the altered hematological parameters and reduced the oxidative stress by decreasing serum levels of TOS and MDA, and increasing the TAC and CAT levels. In addition, histopathological findings supported the aforementioned results. This study concludes that Stellaria media has promising gastroprotective activity against PRX-induced gastric ulcer.