​(Thio)Urea scaffolds are best known for their importance as intermediates in organic synthesis. In this work, a mechanistic study of the reaction between urea (U), (2-hydroxyethyl)urea (U-EtOH) and thiourea (tU)/NaH in DMSO with CO₂ was carried out. While both U/tU reacted with CO2 via a 1 : 2 mechanism through the formation of the keto (thio)carbamide–carboxylate adducts (k-U/tU-CO₂ Na⁺), U-EtOH gave mixed CO₂-adducts composed of organic carbonate and carbamide–carboxylate moieties (Na+-CO2-U-Et-OCO₂ Na⁺). Moreover, we recorded for the first time, a new type of bond, namely sodium carbamimidothiocarbonate (e-tU-SCO₂ Na⁺), upon bubbling CO₂ in the DMSO solution of tU due to the persistence of the enol form (e-tU) and the better nucleophilicity of sulfur over nitrogen focal points. The reaction mechanisms were proven by 1D and 2D nuclear magnetic resonance (NMR) and ex situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopies. The stability of these bonds was studied following the changes in ¹H-NMR as a function of temperature, which indicated the reversibility of these reactions. Furthermore, the proposed mechanisms were explored theoretically via density functional theory (DFT) calculations by analyzing the energetics of ​the anticipated products.