The PCA affirms the classical Nicene and Athanasian formulation of the Trinity: God exists eternally as three distinct persons (Father, Son, Holy Spirit) in one substance or essence. The PCA explicitly endorses the filioque clause, teaching that the Holy Spirit proceeds from both the Father and the Son.

This doctrine is grounded in the Westminster Confession of Faith (II.3) and is considered essential to Reformed theology. The three persons are coequal in power and glory, though they have distinct roles in the economy of salvation.

The PCA holds to the traditional affirmation of divine simplicity and rejects any modalism or subordinationism that would undermine the full deity and equality of all three persons.