This Letter describes a direct measurement of the W boson total decay width, ΓW, using the Collider Detector at Fermilab. The measurement uses an integrated luminosity of 90pb−1, collected during the 1994–1995 run of the Fermilab Tevatron pp¯ collider. The width is determined by normalizing predicted signal and background distributions to 49 844 W→eν candidates and 21 806 W→μν candidates in the transverse-mass region MT<200 GeV and then fitting the predicted shape to the 438 electron events and 196 muon events in the high- MT region, 100<200 GeV. The result is ΓW=2.04±0.11(stat)±0.09(syst)GeV.