This article considers the positions of Gabriel Marcel and Thomas Aquinas on self-knowledge and argues for a synthesis between them. The basis of this Marcelian-Thomistic synthesis is their common understanding of the self as inherently in relation to that which is other (via embodiment) and in the necessity of activation for self-knowledge to occur. The divergence between these thinkers occurs in regard to the process of activation. While Aquinas presents an Aristotelian account of activation rooted in his understanding of cognition, Marcel offers a broader vision of activation that gives pride of place to inter-subjectivity. A Marcelian-Thomistic synthesis preserves the Aristotelian systematization of Aquinas, while adding Marcel's expanded understanding of activation and his prioritization of intersubjectivity. Such a synthesis allows for a treatment of self-knowledge that is metaphysically systematic and true to lived experience.