Despite advances in behavioral and pharmacological treatment for tobacco use and dependence, quit rates remain suboptimal. Increasing physical activity has shown some promise as a strategy for improving cessation outcomes. However, initial efficacy studies focused on intensive, highly structured exercise programs that may not be applicable to the general population of smokers. We describe the rationale and study design and report baseline participant characteristics from the Lifestyle Enhancement Program (LEAP), a two-group, randomized controlled trial. Adult smokers who engaged in low levels of leisure time physical activity were randomly assigned to treatment conditions consisting of an individualized physical activity intervention delivered by health fitness instructors in community-based exercise facilities or an equal contact wellness control. All participants received standard cognitive behavioral smoking cessation counseling combined with nicotine replacement therapy. The primary outcomes are seven-day point prevalence abstinence at seven weeks, six- and 12 months. Secondary outcomes include self-reported physical activity, dietary intake, body mass index, waist circumference, percent body fat, and nicotine withdrawal symptoms. Participants consist of 392 sedentary smokers (mean [standard deviation] age = 44.6 [10.2] = years; 62% female; 31% African American). Results reported here provide information regarding experiences recruiting smokers willing to change multiple health behaviors including smoking and physical activity.