The safe handling of heavy metals and antibiotics during waste disposal has attracted wide attention. In the present study, hydrothermally treated sewage sludge was used for co-pyrolysis with different concentration ratios of pig manure at 600 °C for heavy metal immobilization and antibiotic removal. Heavy metals (except Cd) were mainly retained in the biochar samples due to a high degree of decomposition characteristic of organic matter. Pyrolysis significantly immobilized the heavy metals via converting unstable F1 + F2 + F3 fractions (acid-soluble fraction + reducible fraction + oxidizable fraction) to stable F4 fraction (residual fraction), and more pig manure addition led to improved immobilization performance. After co-pyrolysis, the potential environmental risk of feedstocks reduced significantly and the addition of 50 wt.% of pig manure gave a minimum potential ecological risk index of 10.36 with a low risk of contamination. In addition, six types of antibiotics in feedstocks were decomposed completely during pyrolysis. The co-pyrolysis process showed numerous advantages in the synthetic treatment of sewage sludge and pig manure by reducing the heavy metal toxicity and antibiotic levels.