This study evaluated whether a three-month smartphone-supported daily walking intervention could improve physical activity, psychological well-being, and body composition in adults with cardiometabolic disease. Participants had cardiovascular disease and/or type 2 diabetes and used the Walk15 smartphone platform to monitor daily step count. The intervention aimed to increase daily walking by approximately 1,000 steps per day through individualized step goals, self-monitoring, and digital feedback. Outcomes were assessed before and after the intervention and included daily step count, body composition, handgrip strength, sleep duration, eating behaviors, subjective well-being, vigor, stress, anxiety, health, and happiness.