AbstractThe CUPID-Mo experiment to search for 0$ν β β $ ν β β decay in $^{100}$ 100 Mo has been recently completed after about 1.5 years of operation at Laboratoire Souterrain de Modane (France). It served as a demonstrator for CUPID, a next generation 0$ν β β $ ν β β decay experiment. CUPID-Mo was comprised of 20 enriched $\hbox {Li}_{{2}}$ Li 2 $^{100}$ 100 $\hbox {MoO}_4$ MoO 4 scintillating calorimeters, each with a mass of $∼ 0.2$ ∼ 0.2 kg, operated at $∼ 20$ ∼ 20 mK. We present here the final analysis with the full exposure of CUPID-Mo ($^{100}$ 100 Mo exposure of 1.47 $\hbox {kg} \times \hbox {year}$ kg × year ) used to search for lepton number violation via 0$ν β β $ ν β β decay. We report on various analysis improvements since the previous result on a subset of data, reprocessing all data with these new techniques. We observe zero events in the region of interest and set a new limit on the $^{100}$ 100 Mo 0$ν β β $ ν β β decay half-life of $T_{1/2}^{0ν }$ T 1 / 2 0 ν $> {1.8}\times 10^{24}$ > 1.8 × 10 24 year (stat. + syst.) at 90% CI. Under the light Majorana neutrino exchange mechanism this corresponds to an effective Majorana neutrino mass of $\left<m_{β β }\right>$ m β β $<~{(0.28{-}0.49)} $ < ( 0.28 - 0.49 ) eV, dependent upon the nuclear matrix element utilized.