Background and Objectives Plant protein products are now considered sustainable substitutes for animal proteins in new product formulations, and various methods such as ultrasound have been used to improve their properties. The aim of this study was to investigate the physicochemical and functional properties of grass pea (Lathyrus sativus L.) protein isolate was extracted, as a promising source of plant‐based protein, using conventional (CP), pre‐ultrasonic (PUP) and ultrasound‐assisted (UAP) treatments. Findings Extraction yield, protein content, and protein yield of ultrasound treatments were increased. Ultrasound treatments improved the functional properties of pea protein. Thermal and surface properties were also altered due to the conformational changes in protein molecules during sonication. According to sodium dodecyl sulfate‐polyacrylamide gel electrophoresis, there were no differences in protein fractions of different samples in terms of molecular weight, and protein fractions between 23 and 100 kDa were observed. However, Fourier transform infrared spectroscopy results revealed changes in different treatments suggesting that sonication changed protein secondary structures. Correspondingly, optical and fluorescence microscopy images of protein solutions and foams revealed changes in the structure of proteins and CP presented larger protein aggregates and larger foam bubble sizes than PUP and UAP. Conclusions Ultrasound treatment could increase extraction and improve the functionality of proteins which was attributed to changes in the secondary structure of proteins. Significance and Novelty Grass pea protein isolate can be considered a novel source of valuable protein and ultrasound treatment could enhance the functionality of the protein increasing potential applications of this ingredient in the food industry.