With the rapid development of the exploitation of underground space, more and more large- or superlarge-diameter tunnel-boring machines (TBMs) are being employed to construct underground space projects. At present, because conventional circular TBMs cannot completely meet the requirements of underground space exploitation regarding the cross-section and space-utilization ratio, non-circular TBMs, which are the tunneling equipment for an ideal cross-section, have become the new market growth point. This paper first presents the technical features and development status of non-circular TBMs. Next, in reference to typical projects and technological innovation, this paper investigates key techniques including shield design optimization, multi-cutterhead excavation, special-shaped segment erection, and soil conditioning in loess strata for a rectangular pipe-jacking machine and a horseshoe-shaped TBM, in order to provide a set of feasible solutions for the design, manufacture, and construction of non-circular TBMs. Relevant engineering practice shows that non-circular TBMs with customized design and manufacture have great advantages in terms of construction schedule, settlement control, and space utilization.