We show that electroweak triplet scalar can significantly impact baryogenesis via leptogenesis in concrete and predictive SO(10) GUTs, even when light neutrino masses arise predominantly from the type-I seesaw mechanism. This is illustrated within a minimal renormalisable SO(10) model with 10 and \( \overline{\textbf{126}} \) scalars in the Yukawa sector and a global Peccei-Quinn-like symmetry. The quark-lepton unification and the flavour structure of the fundamental Yukawa couplings enforce type-I dominance in the light neutrino masses, also suppressing the triplet-induced CP asymmetries in the right-handed neutrino decays. However, the triplet’s own decays introduce a new CP-violating source, which can enhance or suppress the total baryon asymmetry. For triplet mass near the right-handed neutrino mass scale, this contribution can dominate, making it essential in assessing the viability of SO(10) leptogenesis scenarios.
