Broadband optical response and strong optical nonlinearity have enabled MXenes to be applied in numerous ultrafast photonic devices. Here, we explored the nonlinear optical properties of a novel MXene, Ta₂C, and demonstrated a femtosecond fiber laser with a Ta₂C-based saturable absorber (SA). First-principles calculations were employed to fully reveal the structural and electronic properties of the Ta₂C MXene. The third-order nonlinear optical properties of the as-prepared Ta₂C nanosheets were measured from the visible to near-infrared regime by the commonly used open-aperture Z-scan technique. Its maximum nonlinear absorption coefficient was fitted to be −0.42 cm/GW, implying its broad application prospects in nonlinear photonic devices. Moreover, Ta₂C MXene-coated microfibers as SAs were integrated into erbium-doped fiber laser cavities. Long-term stable mode-locked pulses centered at 1560.1 nm were generated by the constructed laser device. The ultrashort pulse duration of about 774 fs and high signal-to-noise ratio of over 50 dB indicate that Ta₂C MXene is a promising material for generating ultrafast pulses.