We report the detection of gamma-ray emission from PWN Kes 75 and PSR J1846-0258. Through modeling the spectral energy distribution incorporating the new Fermi-LAT data, we find the the observed gamma-ray emission is likely a combination of both the PWN and pulsar magnetosphere. The spectral shape of this magnetospheric emission is similar to the gamma-ray spectrum of rotation powered pulsars detected by Fermi-LAT and the results from our best-fit model suggest the pulsar's magnetospheric emission accounts for 1% of the current spin-down luminosity. Prior works attempted to characterize the properties of this system and found a low supernova explosion energy and low SN ejecta mass. We re-analyze the broadband emission incorporating the new Fermi emission and compare the implications of our results to prior reports. The best-fit gamma-ray emission model suggests a second very hot photon field possibly generated by the stellar wind of a Wolf-Rayet star embedded within the nebula, which supports the low ejecta mass found for the progenitor in prior reports and here in the scenario of binary mass transfer.