Schoenoplectus californicus, a macrophyte from Peruvian marine–coastal wetlands, is traditionally used for medicinal purposes, yet its pharmacological potential remains insufficiently explored. This study evaluated the chemical profile, antioxidant capacity, psychopharmacological effects, and analgesic activity of a hydroethanolic extract from its rhizomes. Phytochemical screening and LC–MS/MS analyses were performed to characterize secondary metabolites. Antioxidant activity was assessed using DPPH and ABTS assays, while in vivo anxiolytic, sedative, and analgesic effects were evaluated in Balb/c mice through open field, elevated plus maze, rotarod, analgesimeter, tail-flick, and hot plate tests, with diazepam and tramadol as reference drugs. In silico PASS and BOILED-Egg analyses were used to predict pharmacological mechanisms and central nervous system permeability. The extract contained flavonoids, phenolic compounds, and stilbenes and exhibited notable antioxidant activity (IC₅₀: 0.7319 mg/mL for DPPH and 0.6207 mg/mL for ABTS). Anxiolytic effects were observed at 50 mg/kg, sedative effects at 200 mg/kg, and significant analgesic activity at 50 mg/kg. Several compounds were predicted to cross the blood–brain barrier, with inhibition of GABA aminotransferase suggested as a potential mechanism. Acute toxicity was detected (LD₅₀ > 2000 mg/kg). These findings support S. californicus as a promising source of neuroactive and analgesic compounds, although further mechanistic and dose-optimization studies are required.