We fabricated buried circular cladding waveguides with different cross-sectional diameters in neodymium-doped yttrium aluminate crystals via femtosecond laser direct writing at a repetition rate of 500 kHz. Continuous-wave waveguide lasers operating at 1079 nm were successfully achieved at room temperature using an optical pump with 803-nm light. In addition, the guiding properties of the cladding waveguides fabricated using various laser-writing conditions were investigated. The fabricated waveguides exhibited excellent performance, with an insertion loss of 1.2 dB at a wavelength of 1.06 μm. Confocal micro-Raman and micro-photoluminescence analyses were performed to investigate the crystalline lattice modifications induced by the FsLDW. The lasing slope efficiency of the cladding waveguide with a diameter of 40 μm reached 29.2% with a maximum output power of 183 mW, and the cladding waveguide with a diameter of 60 μm exhibited a lasing slope efficiency of 29.9% and a maximum output power of 155 mW.