The composition and valence electrons of molecules usually have a great impact on the eventual topology. With a high tendency to form sp/sp²-hybridized multiple bonding of C₂, the main-group dicarbides (C₂X_n) usually adopt a non-closo (or open) topology. By contrast, naked Zintl ions (e.g., Si₅²⁻) usually feature deltahedral structures. In this paper, we report an unexpected example of a pentatomic carbon-silicon cluster C₂Si₃²⁻ which has the global minimum C₂Si₃²⁻-01 featuring a closo-structure with all deltahedras. The global minimum nature of C₂Si₃²⁻-01 was confirmed by various sophisticated methods including G3B3, G4, CBS-QB3 and W1BD as well as CCSD(T) extrapolated up to the complete basis set limit based on the CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ and CCSD(T)/aug-cc-pV5Z calculations. The AdNDP analysis revealed that C₂Si₃²⁻-01 possesses a lone pair of electrons on each of the three silicon atoms, four 2c–2e bonds and four 3c–2e bonds, among which the two 2c–2e bonds between the two carbons indicate the existence of a multiply bonded C₂ (1.320 Å) that carries the most negative charges. With a total of 22 valence electrons, C₂Si₃²⁻-01 formally resembles the known Wade–Mingos clusters with (n + 1) polyhedral skeletal electron pairs (PSEPs). Replacement of Si₂ by the highly electron-withdrawing C₂ does not break the deltahedral topology of the Zintl ion Si₅²⁻. To the best of our knowledge, C₂Si₃²⁻ represents the smallest deltahedral main-group dicarbide and also the first deltahedral main-group dicarbide with (n + 1) PSEPs. To direct its organometallic applications, we designed the hetero-deckered sandwich compounds CpMg(C₂Si₃²⁻)MgCp, in which the C₂Si₃²⁻-01 unit can be nicely maintained.