The present work aims to evaluate the effect of re-treated urban wastewater using wood biochar on the development of maize (Zea mays L.) plants. Maize seeds were sown in plastic pots, containing agronomic soil, and watered with treated wastewater (TWW) before and after re-treatment with wood waste biochar. Before re-treatment, results indicated that the application of TWW at 75% significantly enhanced the maize growth, in terms of plant height, shoot fresh (SFW) and dry (SDW) weight compared to control (natural water). While, the application of TWW at 100% showed the opposite effects. In fact, the total chlorophyll content and relative water content (RWC) were significantly decreased by 20% and 4%, respectively, compared to control plants. Furthermore, TWW at 100% significantly (p < 0.05) induced an accumulation of oxidative stress markers (MDA, H2O2). The non-enzymatic antioxidant process (total polyphenols and flavonoids) and the enzymatic antioxidant activity (CAT and APX) were also interestingly increased. The obtained negative correlation between maize growth and the accumulation of oxidative stress markers could explain the showed reduction in maize growth under 100% TWW. However, this effect seems to be alleviated in maize plants when they were watered with TWW re-treated with biochar, indeed, a significant improvement was marked in plant height, SFW, SDW, total chlorophyll content and RWC by 44%, 106%, 176%, 38% and 12%, respectively, compared to maize under 100% TWW. The finding suggests that the use of TWW diluted or re-treated by wood biochar could be a relevant approach to valorize TWW in agricultural purposes.