This paper seeks to evaluate the impact of a thixotropy-enhancing agent (TEA) on the variations in thixotropy and formwork lateral pressure of self-consolidating concrete (SCC) with 650 ± 15 mm (24.3 ± 0.6 in.) slump flow consistency. Six mixtures containing various TEA concentrations along with either a melamine- or polycarboxylate-based high-range water-reducing admixture (HRWRA) were tested. The results are compared with similar SCC mixtures made with conventional viscosity-enhancing admixtures (VEAs), including a liquid polysaccharide, powder polysaccharide, and cellulose-based. Test results show that the use of TEA can significantly increase the degree of thixotropy and reduce the formwork pressure compared with similar mixtures containing conventional VEAs. This is attributed to the thixotropic nature of this agent that enables the material to rapidly recover its cohesiveness following some time at rest. The combination of TEA with either powder polysaccharide or cellulose-based VEA at low concentration was found to reduce the maximum initial pressure and increase the rate of pressure drop with time compared with SCC containing only conventional VEA at similar concentration. The TEA/VEA combinations resulted in better fluidity retention with time. A good relationship exists between the lateral pressure and thixotropy determined from SCC mixtures containing various concentrations of TEA and/or low concentrations of conventional VEA. The higher the degree of thixotropy, the less the mixture develops lateral pressure. This is attributed to the reversible effect of thixotropy that enables the material to increase its shear strength properties after some resting time.