Objective: To evaluate the effectiveness of the ‘Healthy Dads, Healthy Kids (HDHK)’ program when delivered by trained facilitators in community settings. Method: A two-arm randomized controlled trial of 93 overweight/obese fathers (mean [SD] age = 40.3 [5.3] years; BMI = 32.5 [3.8] kg/m2) and their primary school-aged children (n = 132) from the Hunter Region, Australia. In 2010–2011, families were randomized to either: (i) HDHK intervention (n = 48 fathers, n = 72 children) or (ii) wait-list control group. The 7-week intervention included seven sessions and resources (booklets, pedometers). Assessments were held at baseline and 14-weeks with fathers' weight (kg) as the primary outcome. Secondary outcomes for fathers and children included waist, BMI, blood pressure, resting heart rate, physical activity (pedometry), and self-reported dietary intake and sedentary behaviors. Results: Linear mixed models (intention-to-treat) revealed significant between-group differences for fathers' weight (P < .001, d = 0.24), with HDHK fathers losing more weight (− 3.3 kg; 95%CI, − 4.3, − 2.4) than control fathers (0.1 kg; 95%CI, − 0.9,1.0). Significant treatment effects (P < .05) were also found for fathers' waist (d = 0.41), BMI (d = 0.26), resting heart rate (d = 0.59), energy intake (d = 0.49) and physical activity (d = 0.46) and for children's physical activity (d = 0.50) and adiposity (d = 0.07). Discussion: HDHK significantly improved health outcomes and behaviors in fathers and children, providing evidence for program effectiveness when delivered in a community setting.