The incorporation of fibre into pea protein matrices influences their microstructure, yet our understanding of their gut fermentability remains unexplored. In this study, dietary fibres and protein from yellow pea were investigated for their physico-chemical properties and impact on in vitro colonic fermentation using human inoculum. Pea fibre and pea protein blends were studied at different pH and after thermal treatment at 95 °C for 30 min with oscillatory rheology, static light scattering and confocal laser scanning microscopy. The effect on in vitro colonic fermentation was evaluated measuring gas production, ammonia, and short chain fatty acid (SCFA) production. Rheology indicated that during thermal treatment a firmer gel is formed close to the protein isoelectric point with a structure characterised by aggregation, but less particle swelling compared to other pH. Addition of fibre led to higher storage modulus (G′), with the fibre dominating the rheological properties. Fermentation of samples containing protein led to higher levels of ammonia and SCFA compared to only fibres. Blends produced higher amounts of valerate, i-valerate and caproate, and lower amounts of ammonia. Reduced fermentation of proteins in the presence of fibres was also reflected in a more intact microstructure of the protein particles in the digesta. Although thermal treatment of blends caused particle swelling and induced gelation, only small differences could be discerned in the in vitro colonic fermentation outcomes. Our results highlight that potentially harmful fermentation products from protein, such as ammonia, were reduced in the presence of pea hull fibre.