A dispersion-engineered artificial transmission line (TL) enabled by negative group delay (NGD) is proposed to exhibit squint-free dominant mode leaky-wave radiation. The unit cell of the proposed artificial TL is based on a multi-section directional coupler, which is used to generate the desired NGD, followed by a composite right/left-handed transmission line (CRLH-TL) structure. An amplifier is incorporated within each unit cell to compensate for the power loss from the NGD coupler. By incorporating the NGD response, the resulting artificial TL can demonstrate a dispersionless fast wave characteristic within the NGD frequency band. For proof-of-concept, prototypes of a single unit cell and a three-unit cell NGD artificial TL are fabricated and tested to verify the dispersion and radiation characteristics. The measured radiation patterns of the proposed NGD artificial TL indicate that the main beam angle is located at -35 degrees in the backward direction, with a squint-free bandwidth from 2.55 GHz to 2.75 GHz.