This study evaluated the effects of a dietary mixture based on extruded linseed and pea (ELP; 20:80 w/w) and probiotics (L. acidophilus) on the performance, biochemical responses, breast muscle fatty acids (FA) profile, and lipid indices in broiler chickens. A total of 480 one-day-old Ross 308 broilers were assigned into four groups in a 2 × 2 factorial arrangement with two levels of ELP (0% and 30%) at the expense of soybean meal, corn, and vegetable oil and two levels of probiotic (0 and 20 g ton−1 feed). There were no effects of ELP diet or probiotic supplementation on performance and carcass traits. Feeding the ELP diet increased plasma total protein, urea nitrogen (PUN), and creatinine (Cre) levels with no changes in the PUN/Cre ratio. A probiotic addition lowered the total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and the TC/HDL-C and LDL-C/HDL-C ratios. The ELP diet improved the breast muscle FA profile by lowering total saturated FA (SFA) and increasing total polyunsaturated FA (PUFA), omega-3 (n-3), unsaturated FA (UFA), PUFA/SFA, and UFA/SFA ratios. Probiotics increased total PUFA, omega-6 (n-6) and decreased the n-6/n-3 ratio, total UFA, and UFA/SFA ratio. Dietary treatment interaction exhibited a synergistic effect for total PUFA and an antagonistic effect for n-3 PUFA and n-6/n-3 PUFA ratio in breast muscle. Probiotics reduced some lipid indices (PUFA/SFA ratio, desirable FA and nutritive value index) only when ELP0 was fed. In conclusion, based on these results, using ELP30 alone in broiler diets is recommended to improve meat’s nutritional value for consumers.