Background The aim of this study was to evaluate the influence of psychological stress on non‐surgical periodontal treatment (SRP) outcomes in patients with severe chronic periodontitis (stage 3/4 generalized periodontitis) at 6 months in the French population. Methods Patients diagnosed with severe generalized chronic periodontitis (periodontitis stage 3/4) were included in this study. At baseline, psychological status was evaluated by self‐administered questionnaire (Depression Anxiety Stress Scale 42 [DASS‐42] and Toulouse coping scale [TCS]). Plasma levels of cortisol and chromogranin‐A were determined. Patients were then managed by oral hygiene instructions, scaling and root planing of sites with PD >3 mm and followed at 3 and 6 months. Quantitative and qualitative variables were described and interactions were determined by linear and logistic regressions. Results Seventy‐one patients were included in this study and 54 were followed up to 6 months. An average probing depth (PD) reduction of 0.73 ± 0.11 mm and decrease of diseased sites (PD >3 mm) were measured at 6 months illustrating SRP efficacy. Multivariable analysis showed that increased DASS‐stress score was associated to worsened SRP outcomes in terms of bleeding on probing (BOP) (OR = 1.02, P <0.05) and mean PD (P <0.05) reduction. An increase of DASS‐depression score negatively influenced PD >5 mm (OR = 1.06, P <0.05), PD >7 mm (OR = 1.17, P <0.01), CAL >5 mm (OR = 1.03, P <0.05), and CAL >7 mm (OR = 1.07, P <0.05) reduction. Negative coping strategies were also associated with worsened SRP outcomes. Conclusions Patients with increased stress, anxiety, and depression scores as well as those exhibiting negative coping strategies demonstrate worsened SRP outcomes. DASS‐42 and TCS were useful to determine psychological status and their use could be incorporated to assess treatment prognosis.