Complexed heavy metal (HM) in acidic wastewater is one of the toughest issues for environmental pollution control. Aimed at directly eliminating complexed HMs from acidic wastewater, a novel cost-effective oligo-dithiocarbamate (oligo-DTC) chelating precipitant was synthesized by a bottom-up method from ammonia and 1,2-dichloroethane (DCE). Synthesis conditions were systematically optimized based on Ni removal performance at pH 2 and pH 7. An NH3/DCE ratio of 3:1 or above at temperatures between 100 and 160 °C were suitable for amination, while a NaOH/DCE ratio of 0.5–1.0:1 and a CS2/DCE ratio of 1.0:1 were favorable for dithiocarbamylation. The theoretical S/Ni mole ratio of oligo-DTC, representing the theoretically required oligo-DTC dose for complete Ni removal, was 8.2–9.4 at pH 2 and 4.0–4.6 at pH 7. Oligo-DTC showed high removal efficiencies for various HMs and had advantages over similar DTCs with high synthesis costs. Oligo-DTC successfully removed complexed HMs from two typical acidic wastewaters with residual HMs below the stringent discharge limits. Oligo-DTC had an average molecular weight of 1150 Da based on LCHRMS. Characterizations (scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy) showed that oligo-DTC removed HMs by chelation with its NCS2– functional groups and also indicated that oligo-DTC suffered nonnegligible self-aggregation and decomposition in HM removal under strongly acidic conditions.