Background In many low resource settings, the provision of government mental health care services is limited to specialized psychiatry units in urban hospital care facilities, where the most common treatment for common mental disorders (CMDs) is pharmacotherapy, occasionally with adjunct nonspecific psychological support. We aimed to evaluate the effectiveness of adding a low intensity, psychological intervention, Problem Management Plus (PM+) for CMDs into routine care in a specialized mental health care facility in Pakistan. Methods A two arm, single-blind individual randomized controlled trial (RCT) was carried out with adults (N=192), referred for psychological support by psychiatrists. The study participants were randomized (1:1) to PM+ plus Treatment as Usual (TAU) (n = 96) or TAU only (n = 96). The primary outcomes were symptoms of anxiety and depression, measured by the Hospital Anxiety and Depression Scale (HADS) and functional impairment as measured by WHO Disability Assessment Schedule (WHODAS-12) at 20-weeks after baseline. Results The analysis was done on intention-to-treat principle. The linear mixed model analysis showed that at 20-weeks after baseline, there was a significant reduction in symptoms of anxiety and depression (mean [SD], 16.23 [8.81] vs 19.79 [7.77]; AMD, -3.10; 95% CI, −0.26 to −5.76); p =0.03 and improvement in functioning (mean [SD], 22.94 [9.37] vs 27.37 [8.36]; AMD, -4.35; 95% CI, -1.45 to -7.24); p =0.004 in PM+ plus TAU versus TAU group. The follow-up rate was 67% at primary end-point. Conclusions Specialized care facilities in LMICs may consider adding brief, evidence-based psychological treatments for CMDs to their routine care.