The purpose of this study was to prepare and evaluate the chemical and physical properties of protein-polyphenol-polysaccharide ternary soluble complexes composed of pea protein isolate (PPI), quercetin (Q) and mesquite gum (MG). PPI and MG were mixed in varying ratios at pH 5.0 and hydrodynamic diameter, ζ-potential, turbidity and soluble complexes yield were used to identify the optimal PPI:MG ratio (1:3 PPI:MG). A pH range of 3.0–7.0 was tested to find the optimal pH to form the soluble complexes using the previously mentioned ratio. Turbidity, hydrodynamic diameter and ζ-potential measurements were used for establishing the optimal pH (5.0) leading to the formation of soluble complexes which exhibited a hydrodynamic diameter of 333 ± 15 nm and ζ-potential of −19.00 ± 0.20 mV. The binding constant and number of binding sites of Q with PPI determined by fluorescence were 10.007 × 104 M−1 and 1.095 at 25 °C, respectively. Ternary complexes between PPI-Q-MG had a hydrodynamic diameter of 134 ± 7 nm, ζ-potential of −19.65 ± 0.21 mV, encapsulation efficiency of 89.83 ± 0.24%, scavenging activity of 36.09 ± 1.38% measured by ABTS, provided strong protection against UV-light degradation, and exhibited high physical stability during 28 days at 4 °C. The present work revealed that ternary complexes could be an effective delivery system for bioactive compounds with applications in a wide range of functional foods and beverages. Display omitted •Soluble complexes were formed using pea protein, mesquite gum and quercetin.•Diameter, ζ-potential and yield were used to find the optimal polymer ratio.•Optimal pH and PPI:MG ratio for complex formation was 5 and 1:3, respectively.•PPI-MG nanocomplexes efficiently encapsulated and protected quercetin.•Ternary soluble complexes could be an effective delivery system for bioactive compounds.