A history of anterior cruciate ligament reconstruction (ACLR) and high body mass index (BMI) are strong risk factors for incident knee osteoarthritis. Limited research has evaluated the interaction between ACLR and high BMI on limb-level loading and early deleterious changes in cartilage health. The purpose of this study was to separately investigate the association between vertical ground reaction force (vGRF) loading profiles during gait and tibiofemoral cartilage composition in ACLR patients with high and normal BMI. Forty-three participants with primary unilateral ACLR (17 ± 14 months post-ACLR) were categorized as high (≥ 25 kg/m²;​ n = 18) or normal (< 25 kg/m²;​ n = 25) BMI and performed an overground gait at self-selected speed. For biomechanical outcomes, we calculated the differences between first peak and midstance minimum (∆vGRF1) and between the second peak and midstance minimum (∆vGRF2). T1ρ relaxation time interlimb ratios (ILR), calculated as the T1ρ relaxation time in the ACLR relative to the uninjured limb, were calculated for the medial and lateral tibia and femur. Stepwise linear regressions were used to determine associations between biomechanical outcomes and T1ρ relaxation time ILR for each region of interest. Lesser ∆vGRF1 and ∆vGRF2 in the high-BMI group significantly associated with greater T1ρ relaxation time ILR for the medial femoral condyle (ΔR² = 0.28, p = 0.03;​ ΔR² = 0.25, p = 0.04, respectively) and tibial plateau (ΔR² = 0.55, p < 0.001;​ ΔR² = 0.25, p = 0.004, respectively). Aberrant limb-level loading, characterized by less dynamic limb loading, is linked to deleterious changes in tibiofemoral cartilage in ACLR patients with high BMI, suggesting that gait retraining may be more critical for ACLR with a BMI ≥ 25 kg/m².