The study was designed to evaluate the effects of timing and duration of low voltage electrical stimulation (LVES) of light and heavy beef carcasses on meat and carcass quality of South African commercial feedlot cattle. It was inspired by the variations in meat quality that were emanating from the various electrical stimulation protocols by meat processors and the negative impact of this quality variation on the profitability of the meat industry. It was also inspired by the increasing live and carcass weight of cattle owing to better nutritional interventions and the use of feed additives and the impact on post-slaughter processing in relation to meat quality. It is believed that more meat could be produced from fewer heavier cattle compared with larger number of smaller or lighter cattle. However, the quality of meat, for example, shear force (SF), water holding capacity (WHC), drip loss (DL) and colour, from these heavier animals needs to be evaluated in order to ascertain the advantages and/or disadvantages, compared with lighter carcasses. To better understand the effects of treatments on meat quality, proteolytic enzyme activity, muscle energy metabolites and histological parameters were evaluated. Carcasses were subjected to LVES (110 V) applied early (7 min) or late (45 min) post-mortem (pm), for shorter (30 s) or longer (60 s) duration on heavy or lighter carcasses. Meat quality evaluations were done to ascertain the effects of the treatments (i.e. carcass weight, ES duration and time of ES application) and their interactions at 3 and 14 days pm (dpm). This was done to determine the values of the various quality parameters at the abattoir/butchery (3 dpm) and display period (14 dpm). Analyses revealed that early application of electrical stimulation (ES), especially on the heavier carcasses produced the highest rigor temperature (> 35 ᴼC), which produced the lowest (P < 0.05) meat SF at 3 and 14 dpm. However, early ES application was disadvantageous for meat WHC and DL, as higher (P < 0.05) DL and lower WHC were recorded, especially in the heavier carcasses. The interaction of shorter ES and heavier carcass weight favoured (P < 0.05) meat SF at 3 days pm. Longer ES did not favour WHC at 3 and 14 dpm. Heavier carcasses exhibited lower (P < 0.05) WHC and higher DL at 3 dpm, but at 14 days of ageing, there were no significant differences between the two weight categories. In terms of meat lightness (L*), early ES and longer ES produced the lightest (P < 0.05) meat at 2 and 14 dpm regardless of carcass weight. The interaction of early ES and longer ES also produced the highest (P < 0.05) L* at 2 and 14 days pm. Early ES produced the highest (P < 0.05) chroma (C*), at 2 dpm. The interaction of early ES and heavier carcasses also produced a significantly higher (P < 0.05) C* at 2 days pm. On the other hand, the interaction of late application and longer duration of ES produced higher (P < 0.05) C* at the display period (14 dpm). Regarding hue angle (H*), early ES produced higher (P < 0.05) H* at 2 dpm, but at 14 days pm, late ES produced higher (P < 0.05) H*. Heavier carcasses exhibited higher but not significant H* at 2 dpm, but at the display period, heavier carcasses exhibited lower (P < 0.05) H*. Furthermore, the interaction of early ES and longer duration of ES brought about higher (P < 0.05) H* at 2 and 14 dpm. Overall, early LVES on heavier carcasses favoured SF and C* especially at the butchery period but as the meat aged, the advantages diminished. Drip loss and WHC were also marginally disadvantaged by early ES, but these could be minimized by shorter ES. This shows that quality heavier carcasses, which favour slaughter house pricing, could be produced and processed alongside smaller carcasses with better managed LVES. The use of LVES has the potential to reduce variability in meat quality while reducing occupational risk to meat workers.