It has been said that the Reformed notion of union with Christ is the central framework of T. F. Torrance’s atonement theology. Martin Davis argues that union with Christ is a heuristic, over-arching rubric for the discussion of many themes in Torrance’s soteriology, including incarnational reconciliation, the wonderful exchange, vicarious humanity, onto-relationality, faith, justification and sanctification. Kye Won Lee similarly suggests that the heart of Torrance’s thought is union in Christ and union with Christ. Yet, since union with Christ is a multifaceted concept, it is not possible to fully apprehend its significance without wrestling with the complicated question of which kinds of theological systems embed it. To this end, scholarship has yet to fully explain why Torrance interprets Calvin’s doctrine of union with Christ the way he does. In this paper, I examine how Torrance’s interpretation of Calvin’s teaching on union with Christ, as presented in his 1956 monograph Kingdom and Church: A Study in Theology of the Reformation, diverges from the tradition of Covenant Theology. I shall advance the discussion by demonstrating that this divergence is rooted in Torrance’s reliance on Irenaean soteriology as a underlying force shaping his interpretation, aimed at reconsidering the ordo salutis as established by the tradition of Federal Calvinism. I show that Torrance’s interpretation of Calvin’s teaching on union with Christ, as well as his integration of Calvin’s theology into his own theological project, aligns with his atonement theology as shaped by the biblical and Irenaean understandings of recapitulation.