This study aimed to investigate the effects of dietary phytosterol (PS) supplementation on growth performance, meat quality, and lipid metabolism in finishing pigs and to explore the potential mechanisms. Forty-eight barrows with an initial body weight of 73.96 ± 2.80 kg were randomly allocated to two treatments, with six replicate pens of four pigs per pen: the CON group fed a basal diet, and the PS group fed a basal diet with 300 mg/kg of PS for a period of 42 days. Dietary PS improved the average daily gain, apparent digestibility of ether extract, and jejunal lipase concentration (P < 0.05). Additionally, PS increased the serum high-density lipoprotein cholesterol level, intramuscular fat concentration, and essential fatty acid concentrations in the muscle, including C18:2n6c, C18:3n3, and n-3 PUFAs (P < 0.05). Furthermore, PS upregulated the mRNA expression of genes associated with lipogenesis and transportation, such as acetyl-coenzyme A carboxylase, fatty acid synthase, and peroxisome proliferator-activated receptor γ (P < 0.05), and tended to increase the mRNA expression of cluster of differentiation 36 (CD36; P = 0.09). Colonic microbiota comparisons showed that dietary PS downregulated the relative abundance of Clostridium_sensu_stricto_1, Escherichia-Shigella, and Prevotella_9, while upregulating the relative abundance of unidentified Ruminococcaceae and Paludicola. Correlation analysis indicated that the relative abundance of Prevotella_9 was negatively correlated with the expression of CD36, whereas Paludicola and unidentified Ruminococcaceae were positively correlated with the expression of lipogenic genes. In conclusion, PS can increase growth performance, enhance nutrient digestion, and improve pork quality by increasing intramuscular fat deposition in finishing pigs, a process that involves the regulation of the gut microbiota and lipid metabolism.