Low-temperature chemical vapor deposition (CVD) growth of single-walled carbon nanotubes (SWNTs) was achieved on two different types of CoxMg1−xO catalysts prepared by different techniques: atomic layer deposition (ALD) and impregnation. The chirality distribution of SWNTs grown on the ALD-prepared CoxMg1−xO catalyst is wider than that of SWNTs grown on the impregnation-prepared CoxMg1−xO catalyst. The different chirality distributions of SWNTs are related to their different growth modes. The ALD-prepared CoxMg1−xO catalyzes the growth of SWNTs by “tip growth” mode, as revealed by in situ environmental transmission electron microscopy studies. In contrast, SWNTs grow on the impregnation-prepared CoxMg1−xO by “base growth” mode. “Base growth” is attributed to strong metal–support interactions between the epitaxially formed Co nanoparticles and the underlying MgO support, accounting for the synthesis of SWNTs with high chiral-selectivity. In addition, impregnation-prepared CoxMg1−xO catalysts calcinated at different temperatures were systematically studied and their catalytic performances in synthesizing carbon nanotubes were elucidated. This work illustrates the influence of metal–support interactions and catalyst reducibility on the chirality-distribution of the synthesized SWNTs.