Little is known about the difference in effectiveness of lifestyle intervention between women with PCOS and non-PCOS women. In a post hoc longitudinal analysis of a randomized, controlled trial, we aimed to investigate whether infertile women with PCOS and obesity (N = 87) responded differently to a 6-month lifestyle intervention program than infertile non-PCOS obese controls (N = 172). We evaluated several aspects of the intervention such as changes in diet, physical activity, and dropout rate, as well as the effect on weight, quality of life (QoL), and cardiometabolic outcomes. Multilevel analyses were used, and analyses were adjusted for baseline characteristics such as age, education, and smoking. Although BMI in both groups significantly decreased at 3 months and 6 months, there were no significant differences between the groups at 3 months (adjusted B: −0.3, 95% CI: −0.9 to 0.3, p = 0.35) and 6 months (adjusted B: 0.5, 95% CI: −0.4 to 1.4, p = 0.29). Women with PCOS and non-PCOS women had similar compliance with the lifestyle intervention in terms of actual change in diet and physical activity. Mental QoL scores were not different at either 3 or 6 months. Physical QoL scores were lower in women with PCOS compared with non-PCOS women at 3 months (adjusted B: −2.4, 95% CI: −4.8 to −0.06, p = 0.045) but not at 6 months. Cardiometabolic parameters did not differ between the groups. Our results showed that infertile women with PCOS and obesity and non-PCOS obese controls responded largely similarly to our lifestyle intervention and achieved the same level of improvement in markers of cardiometabolic health.