Herein, we present the results of electrical conductivity studies of single-crystal diamond needles. Pyramid-shaped needles of about hundreds of micrometers in length and about tens of micrometers in thickness were produced by oxidation of polycrystalline diamond films fabricated by chemical vapor deposition. The electrical conductivity of the needles was characterized via current measurements using a field ion microscope in the dark and under laser illumination. Considering the effects of laser intensity and wavelength on the measured current, we determine that the observed conduction regime corresponds to competing Ohmic and Poole-Frenkel conduction mechanisms. The measured values are in good agreement with the values reported previously for bulk and thin film diamond. The model that is proposed explains the electric conduction properties as well as light absorption and subsequent sample heating, with the presence of structural defects and impurities in diamond.