Abstract: This study examines the effects of external electric fields (ranging from -0.04 a.u. to 0.04 a.u.) on the bond length, total energy, dipole moment, energy gap, infrared (IR) spectrum, and potential energy surfaces of nitric oxide (NO) molecule using density functional theory (DFT). All DFT calculations have been performed at the B3LYP level with the D95 (3df, 3pd) basis set. Furthermore, the excited-state properties of NO have been analyzed using the CIS-B3LYP method, also employing with the D95 (3df, 3pd) basis set as well. The results reveal that the ground-state properties of NO are notably affected by the external electric field. As the external electric field strength increases from –0.04 a.u. to 0.04 a.u., several key trends emerge: the total energy of the molecule first rises and then falls; the dipole moment initially decreases before increasing; and the energy gap varies progressively. Concurrently, the charge transfer around both the oxygen (O) and nitrogen (N) atoms increases continuously. Under the influence of external electric fields, the harmonic vibrational frequencies and IR intensities of NO undergo significant changes—indicating that IR intensity can be modulated by the external electric field. Additionally, the external electric field exerts a clear impact on the excitation energy, excitation wavelength, and oscillator strength of NO. These findings collectively suggest that the excited-state properties of NO molecules can be effectively regulated by external electric fields.