In this article, we aim to present a theory of consciousness based on the philosophical ideas of Mullā Ṣadrā that can serve as a foundation for practical life. From among his diverse discussions, we focus on elements of his philosophy that can be used to construct a theory of consciousness and the self as the basis for practical living. The issue is that Mullā Ṣadrā interprets the a priori structure of the "self" or "ego" in terms of immediate knowledge (al-ʿilm al-ḥuḍūrī). From his perspective, in the hierarchy of existence, the "self" does not carry a subjectivist meaning; rather, it represents an intuitive, existential experience of presence. This paper also discusses the views of several Western philosophers on the "I" or "ego" and its role in acquiring knowledge, as well as its mode of existence. A comparison is made between Mullā Ṣadrā's theory and that of the contemporary Western philosopher Sartre, particularly regarding consciousness and the ego, to highlight the innovations in Mullā Ṣadrā's thought. Mullā Ṣadrā presents his profound ideas through logical, ontological, and epistemological arguments, mystical metaphors, and novel abstract concepts. While it is impossible to address all aspects of his theory on the "self" here, we will focus on his description of the reality of the "self" to provide the groundwork for a theory of consciousness and its connection to practical human life. The key finding of this study is that, for Mullā Ṣadrā, the "self," immersed in existence, possesses a conscious presence with existence, and this very consciousness serves as the foundation for real actions in human practical and social life. This presence, akin to Heidegger’s concept of being-in-the-world, entails that the ego exists as an active and genuine reality in the world. According to Sartre, the "ego" becomes an entity whose reality is necessary for its completeness and actively exists in the world. Thus, the "self" or "ego" is transformed into an entity existing in the world, whose existence is entirely a conscious presence in the world. The interaction between this consciousness and the world provides the foundation for human practical and social life.