Electric-field (E-field) and radio influence voltage (RIV) from high voltage transmission line occur due to corona discharge. In this proposed work, the effect of corona discharge on aluminum conductor steel reinforced (ACSR) conductor was deeply investigated and mitigated by coating the polyimide/multiwalled carbon nanotubes (PI/MWCNTs) on the surface of the conductor. Bare and coated ACSR panther conductors were tested for E-field on the surface of the conductor, corona inception voltage (CIV), corona extinction voltage (CEV), and RIV. PI/MWCNT was synthesized and characterized by X-ray diffraction, thermogravimetric analysis, and permittivity and conductivity tests. The impact of MWCNT on corona discharge parameters were realized by loading it in different weight percentages as 1 wt%, 3 wt%, and 10 wt% in PI. It has been observed from the measured value (as per the standard IEC 60060-2) that the E-field was reduced by 8%-23%, RIV was suppressed with a difference of 7-18 dB, and CIV/CEV was improved for nanocomposite coated conductor. To comprehend the reason for the E-field and RIV suppression, permittivity and conductivity tests were performed as per the standard ASTM D5568. Lightning impulse voltage test was also conducted on plane-plane electrode configuration and affirmed that PI/MWCNT material has the capability to withstand lightning discharge plasma.