This study evaluated marbling and meat quality traits in lambs of three genotypes under a uniform high-energy fattening regimen. Male lambs (6–7 months old, n = 12 per group) from purebred Kazakh Finewool (control) and two independent Suffolk × Kazakh Finewool F₁ crossbred lines (Groups 1 and 2) were fed identical diets and raised under the same conditions. Meat samples were analyzed for composition, fatty acid profile, micronutrients, color, visual marbling, and microbiological safety. Group 2 crossbreds had significantly higher intramuscular fat (~9.0%) than the controls (~6.5%) (p < 0.05), with corresponding increases in monounsaturated and polyunsaturated fatty acids. Vitamin A, vitamin E, and zinc levels were also higher in Group 2 (p < 0.05), while other nutrients were similar across groups. All samples had normal pH (~5.7–5.8) and high water activity (~0.985) and met microbial safety standards. Visual marbling was more pronounced in crossbreds, and meat color remained bright red with no significant group differences in redness (a value). These findings suggest that crossbreeding Kazakh Finewool with Suffolk sheep, combined with controlled grain fattening, enhances marbling and nutritional traits without compromising safety or appearance, offering a viable approach to improving lamb meat quality.