—In this paper, a substrate integrated waveguide (SIW) quasi-uniform leaky-wave antenna (LWA) is proposed for a dynamically steerable beam design at a single frequency through the use of a thin layer of nematic liquid crystal (LC) underneath the substrate. The orientation of the LC molecules, and therefore the effective dielectric properties of the LC cell, is controlled via an externally low-frequency, low-strength bias voltage. The radiation occurs through a series of closely placed transverse slots etched on the top plane of the SIW. This antenna was designed to operate based on the fundamental space harmonic (n = 0) in the frequency range between 24.25 GHz and 29 GHz, which covers one of the future 5G frequency bands to be deployed in some parts of the world. This novel antenna design concept was verified numerically using a commercial software based on the Finite Element Method (FEM), and the results are presented and discussed herein.