The present work was undertaken to investigate the effect of different lanthanide promoters on the structure–activity properties of Ni/γ-Al2O3 catalyst for CO2 reforming of CH4. Accordingly, a number of lanthanides, namely Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Tm were incorporated into the Ni/γ-Al2O3 catalyst by means of sol–gel method. An extensive physicochemical characterisation was performed using XRD, TG-DTA, BET surface area, BJH, XPS, Raman, H2-TPR, and TEM techniques. Surprisingly, low initial conversions of CH4 and CO2 were obtained for promoted Ni/γ-Al2O3 catalysts compared with un-promoted catalyst, which is due to the presence of smaller pore sizes in the promoted catalysts. The observed initial activity order for conversions of CH4 and CO2 is un-promoted > Eu > Tb > Ho > Tm > Er > Dy > Pr > Sm > Gd > Nd. Interestingly, promoted Ni/γ-Al2O3 catalysts exhibited an outstanding efficiency in time-on-stream studies up to 60 h than the un-promoted catalyst. This significant observation is mainly due to low amounts of amorphous coke deposited on the surface of promoted Ni/γ-Al2O3 catalysts compared with un-promoted catalyst. Among all investigated lanthanides, the Er-promoted Ni/γ-Al2O3 catalyst showed the best performance in CH4 conversion, which is attributed to optimum Ni particle size, more reducibility, and low amounts of amorphous coke formation. It was shown that the catalytic efficacy of Ni/γ-Al2O3 catalysts is highly dependent on the nature of the promoter. These notable findings are expected to bring new opportunities in the design of novel promising catalytic materials for CO2 reforming of CH4.