Lavender essential oil (LVEO) (Lavandula angustifolia L) was investigated for its impacts on broiler chicken growth, intestinal histomorphology, blood biomarkers, and immunological status. Four hundred 3-days-old male chicks (ROSS 308 broilers) (91.47 ± 0.15 g) were randomised to receive four test groups and nourished on basal diets having four levels of LVEO: 0, 200, 400, and 600 mg Kg−1 over 35 days. Dietary addition of LVEO linearly increased the body weight and weight gain during the grower period, while its addition did not affect the overall growth performance. Dietary LVEO increased the villous height, and the higher villous height was detected in the LVEO600 group. Dietary LVEO increased cluster of differentiation (CD3 and CD20) immunoexpression within the spleens of birds given LVEO400 and LVEO600 diets. Serum triiodothyronine and thyroxine hormone levels were the highest in the LVEO400 and LVEO600 groups. LVEO supplementation raised serum growth hormone levels in a dosage-dependent manner. The serum concentrations of glucose and leptin hormone did not vary significantly between the LVEO-supplemented and LVEO0 groups. All levels of supplemental LVEO diminished serum cholesterol, triglyceride, and low-density lipoprotein cholesterol levels, while raising the high-density lipoprotein cholesterol concentration. Total protein values were augmented in all LVEO groups, with the highest concentrations of albumin and globulin in the LVEO600 group, followed by the LVEO400 group. Supplemental LVEO increased serum concentration of complement 3, interleukin- 10, and lysozyme activity in a level-dependent manner. Modifications in the birds’ physiological activities, blood biochemical, intestinal morphological characteristics, and immunological status support the conclusion that dietary LVEO supplementation had numerous positive effects. However, it didn’t influence the birds’ growth.