The seed lectin from Erythrina fusca (EFusL) was purified and characterized to provide an integrated biochemical, structural, and biological profile of this less-described member of the genus Erythrina. EFusL was isolated by affinity chromatography on agarose-lactose and evaluated through hemagglutination assays, physicochemical stability tests, sequence determination, and toxicity assays using Artemia salina nauplii and human cell lines. The purified protein was identified as a 29–31 kDa glycoprotein containing approximately 4.3% neutral carbohydrates and showed specificity for galactosides, with strong inhibition by α-lactose, D-galactose, and GalNAc. EFusL displayed maximal hemagglutinating activity at pH 8.0, retained stability up to 40 °C, and required Ca²⁺ and Mn²⁺ ions for activity recovery. Its 249-amino acid sequence showed high similarity to other Erythrina lectins and conserved key carbohydrate-recognition residues. No toxicity was observed in the tested biological models. These findings indicate that EFusL preserves the canonical legume lectin features and support its potential use as a biochemical and biotechnological tool.