The results of a long-term multiwavelength study the powerful flat spectrum radio quasar 3C 454.3 using {\it Fermi}-LAT and Swift XRT/UVOT data are reported. In $\gamma$-ray band, observations show several major flares when source flux was $>10^{-5}\:{\rm photon\:cm^{-2}\:s^{-1}}$; peak above $141.6$ MeV, $(9.22\pm1.96)\times10^{-5}\:{\rm photon\:cm^{-2}\:s^{-1}}$ observed on MJD 55519.33, corr...