Radiocarbon is one of the most significant radionuclides affecting the safety margins of near-surface repositories for the disposal of low- and intermediate-level, short-lived radioactive waste, arising from the operation and decommissioning of nuclear power plants (NPPs). One of the goals of the present study was to characterize radioactive waste from Ignalina NPP (Lithuania) (storage tanks TW18B01 and TW11B03) from the spent ion-exchange resins/perlite stream to determine the 14C-specific activity of inorganic and organic carbon compounds. The approach applied is based on classical radiochemical separation methods, including acid-stripping techniques and wet oxidation with subsequent catalytic combustion. The suitability of the method for 14C-specific activity determination in ion-exchange resin samples with a minimum detectable activity of 0.5 Bq/g by liquid scintillation counting (LSC) was demonstrated. The extraction efficiency of inorganic and organic carbon compounds based on model samples with known 14C activity was estimated. The fraction of 14C associated with organic compounds ranged from 42% to 63% for storage tank TW18B01 and from 30% to 63% for storage tank TW11B03. The specific activity of inorganic 14C was estimated as 12.6 Bq/g with a relative standard deviation (RSD) of 29% for storage tank TW18B01, and 177.5 Bq/g with a RSD of 35% for storage tank TW11B03. Based on volume and density data, the total 14C activity for radioactive waste stored in tanks TW18B01 and TW11B03 was estimated as 3.59E + 10 Bq (±32%) and 4.15E + 11 Bq (±28%), respectively.