While protein-stabilized emulsions have demonstrated potential for various applications in food, their poor lipid oxidation remains a major challenge. The relationship between the architecture of polyphenolic compounds and their capacity to suppress lipid oxidation has not received extensive scrutiny. In this research, pea protein isolate (PPI)–polyphenol complexes were synthesized to examine their capability of maintaining emulsion stability and suppressing lipid oxidation. The collective evidence from fluorescence spectroscopy and molecular dynamics simulations pointed towards non-covalent and self-initiated interactions between the polyphenols and PPI. The presence of additional hydroxyl groups on the polyphenols could significantly boost the extent of these interactions. Specific clusters in PPI and polyphenols which might have formed hydrogen bonds and hydrophobic interactions. Polyphenols also reduced the interfacial tension and increased the surface hydrophobicity of the complex, thus driving more proteins to adsorb at the oil–water interface. The PPI-rosmarinic acid (RA)-stabilized emulsion had a smaller droplet size and higher electrostatic repulsion, enabling it to resist droplet aggregation. This emulsion stood out as having the most robust stability amongst all PPI-polyphenol emulsions and proved highly efficient in preventing lipid oxidation. This study bolsters the viability of employing polyphenol and pea protein-stabilized emulsions in developing new food products.