An electric wire conductor having both flexibility and a space-saving property. Also provided are a covered electric wire and a wiring harness containing the electric wire conductor. An electric wire conductor contains a wire strand containing a plurality of elemental wires twisted together. The electric wire conductor has a flat portion in which a cross section intersecting an axial direction of the wire strand has a flat shape. Assuming a conductor cross-sectional area of the flat portion as s mm2 and a vacancy ratio defined as a ratio of vacancies not occupied by the elemental wires in a cross section of the flat portion as v %, the conductor cross-sectional area and the vacancy ratio satisfies v>0.29 s+2.0. The covered electric wire contains electric wire conductor and an insulator covering the conductor. The wiring harness contains the covered electric wire.