Reformed Baptists affirm the classical doctrine of the Trinity as formulated in the 1689 London Baptist Confession, Chapter 2. God is one in essence yet subsists in three eternal persons — Father, Son, and Holy Spirit — each fully divine, equally worthy of worship, and possessing the same divine attributes. The doctrine stands firmly within Nicene and post-Nicene ecumenical tradition, inherited through Reformed confessional standards.

The three persons are distinct in their personal properties and relations: the Father is unbegotten, the Son is begotten of the Father, and the Spirit proceeds from both the Father and the Son. This procession of the Spirit (the filioque clause) is affirmed in Reformed Baptist theology, consistent with Western Reformed tradition. Despite the real distinctions between persons, the Trinity maintains strict monotheism and absolute divine unity in power, will, and eternal counsel.

The 1689 Confession explicitly rejects subordinationism, arianism, and modalism. The Trinity is considered foundational to Christian faith and integral to Reformed Baptist soteriology, as the work of creation, redemption, and sanctification is attributed to the unified action of all three persons according to their personal properties.