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Xanthium strumarium was chosen in this study to evaluate its phytoremediation capacity for cadmium, lead, nickel and zinc metals. Five different sites were selected on Faisalabad–Sargodha road (FSR), Pakistan, to monitor the levels of cadmium, lead, nickel and zinc. Leaf and root samples were collected concurrently with soil samples to study the accumulation and tolerance of these metals in X. strumarium. To examine the health of X. strumarium, photosynthetic pigments, free amino acids concentration and total antioxidant activity were also tested. Highly significant concentrations of all metals were recorded in the soil and X. strumarium leaves and roots at all sites as compared to the control. On the average, X. strumarium leaves accumulated 0.27 ± 0.01 mg kg−1 cadmium, 3.33 ± 0.16 mg kg−1 lead, 54.5 ± 1.02 mg kg−1 zinc and 5.85 ± 0.11 mg kg−1 nickel from the soils that have average metal concentration of 0.25 ± 0.24 mg kg−1 cadmium, 3.38 ± 0.29 mg kg−1 lead, 118.7 ± 1.04 mg kg−1 zinc and 4.89 ± 0.12 mg kg−1 nickel. Overall, a slight variation in photosynthetic pigments was noted; however, plants growing at sites with higher metal concentrations exhibited reduced photosynthetic pigments. Increased total antioxidant activity and free amino acids were recorded. X. strumarium leaves showed high accumulation capacity for nickel, cadmium and lead as shown by their highest bio-concentration factors, i.e., 1.651, 1.574 and 1.048 for these metals, respectively. Significant correlations were also found in combinations of these metals in leaves and soils. This study identified X. strumarium as a strong phytoremediator of heavy metals at contaminated roadsides and potentially other areas.