Multiple layers of C250 maraging steel were deposited into a single-wall structure by using wire arc additive manufacturing (WAAM). The microstructural characteristics of the as-deposited C250 steel, in terms of solidification structures and phases, were investigated by using optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The results show that lath martensite and austenite phases are formed in the as-deposited C250 steel. Apart from these two phases, Laves phase Fe2Ti particles, which have not been reported in C250 steel, are also observed in the C250 steel produced by the WAAM process. TEM analysis does not reveal the formation of strengthening precipitates in the as-built C250 steel, which is further confirmed by hardness measurement.