The purpose of the present disclosure is to provide a CNT fiber that is constituted of aligned carbon nanotubes (CNTs), is thin, has little irregularity in thickness, has excellent winding properties when undergoing coiling processing, and has superior conductivity. Provided is a CNT fiber constituted of carbon nanotubes (CNTs) having a thickness of 0.01 μm-3 mm, having a coefficient of variation for irregularity in thickness of 0.2 or less, having a distribution rate a for deviation from roundness of 40% or greater, and a distribution rate b of 70% or greater. Also provided is a method for manufacturing the CNT fiber.