This study aimed to assess socio-demographic correlates of unhealthy lifestyles among adolescents and adults in Ethiopia. A population-based national cross-sectional survey using the WHO NCD STEPS instruments was conducted. Data were collected in 2015, from a total of 9,800 participants aged between 15 and 69 years. Unhealthy lifestyle scores (0 [most healthy] to 5 [most unhealthy]) were determined based on diet (daily fruit and vegetable consumption), smoking status, overweight/obesity, alcohol intake, and physical activity. A co-occurrence of 3 or more unhealthy lifestyles was considered as an unhealthy lifestyle. The study found that 98.2% of participants had low consumptions of fruit and vegetables, 5.4% smoked tobacco, 15.0% consumed excessive alcohol, 66.0% had inadequate physical activity and 2.3% were obese. One in eight (13%) participants were having three or more unhealthy lifestyles. We found that male sex, urban residence, older age, being married or living in common-law, and higher income were associated with unhealthy lifestyles. Participants with higher educational status had lower odds of unhealthy lifestyles. Socio-demographic characteristics such as sex, age, marital status, residence, income, and educational status were correlated with individuals’ lifestyles. Tailored interventions that target specific socio-demographic groups are required to address the increasing burden of unhealthy lifestyles in Ethiopia.