Anti-poverty policies have the potential to improve mental health. We conducted a randomised trial to investigate whether a fourfold increase in the Earned Income Tax Credit (EITC) for low-income Americans without dependent children would reduce psychological distress relative to the current federal EITC available to this population. Between 2013 and 2014, 5,968 participants were recruited; 2,997 were randomly assigned to the treatment group and 2,971 were assigned to the control group. Survey data were collected 32 months post-andomisation (N=4,749). Eligibility for the program increased employment by 1.9 percentage points and after-bonus earnings by 6% ($635 per year) on average over the three years. Treatment was associated with a marginally statistically-significant decline in psychological distress relative to the control group (-0.30 points; 95% CI, -0.63 to 0.03; p=0.076). Women in the treated group experienced a half-a-point reduction in psychological distress (-0.55; 95% CI, -0.97 to -0.13; p=0.032) and noncustodial parents reported a 1.36 point reduction (95% CI, -2.24 to -0.49; p = 0.011) in psychological distress. An expansion of a large anti-poverty program to individuals without dependent children reduced psychological distress for women and noncustodial parents – the groups who benefitted the most in terms of increased after-bonus earnings.