In this paper, the design, fabrication, and experimental validation of a low-profile high-gain metamaterial-assisted slot antenna is presented. Particularly, a subwavelength end-loaded dipole array is designed to realize the required anisotropic zero-index property for the 5.8 GHz wireless local area network (WLAN) band. This metamaterial coating, which operates based on the leaky mode it supports, is applied to a substrate-integrated waveguide (SIW) fed slot antenna. The resulting antenna is only 0.12λ thick, all while accomplishing a broadside gain higher than 10 dBi and a front-to-back ratio larger than 26 dB, which is ∼7 dB and ∼10 dB higher than that of the SIW fed slot alone. The -10 dB impedance bandwidth, which is more than 9%, is maintained the same with or without the presence of the metamaterial coating.