The aim of this study was to determine the relationship between blood pressure (BP) variability and left ventricular (LV) mechanical function in untreated normal-weight, overweight, and obese hypertensive patients. This cross-sectional study included 144 untreated hypertensive study participants who underwent 24-h ambulatory BP monitoring and complete two (2DE) and three-dimensional echocardiography (3DE). All the patients were divided into three groups according to their BMI: normal-weight patients (BMI < 25 kg/m), overweight patients (25 ≤ BMI < 30 kg/m), and obese patients (BMI ≥ 30 kg/m). Daytime, night-time, and 24-h BP variability progressively increased from normal-weight, throughout overweight, to obese hypertensive study participants. 2DE and 3DE LV longitudinal, circumferential and radial strains, as well as 3DE area strain, were significantly lower in obese hypertensive patients than in normal-weight and overweight study participants. 3DE LV volumes indexed for BSA did not differ significantly among the three observed groups. Night-time and 24 h BP variability indices, more than daytime BP variability parameters, were associated with 2DE and 3DE longitudinal and circumferential strains independent of BMI, LV mass index, and average 24-h SBP and DBP values. BP variability and LV deformation are significantly affected by obesity in untreated hypertensive patients. BP variability is associated with 2DE and 3DE LV mechanics independently of main clinical and echocardiographic characteristics.