This critical study develops a theory of the competencies of sustainability leaders, grounded in research. A sustainability leader is generally described as an individual who creates profit for stakeholders, while protecting the environment and improving the lives of those impacted as a result of his/her leadership. The study revealed there is more than one way to be a sustainability leader--different paths can result in decisions and actions that synthesize the needs of, and impacts to, planet, people, and profit. An intention to integrate the imperatives of people, planet and profits--a sense of purpose that transcends all of the behaviors and qualities of a sustainability leader--is an all-encompassing aspect of the theory. In addition, a sustainability leader possesses a systems-thinking style and exhibits positive psychological constructs. The generally adopted sustainability model of three identical-sized circles does not accurately depict how a leader approaches an issue in need of sustainable consideration. The study is of interest to professionals in any discipline with concerns about sustainabiity, as well as to scholars studying leadership approaches.