Charged lepton flavor violation is a clear signal of new physics. Such decays are not allowed in the Standard Model but highly anticipated in a large class of new physics models. A direct search for lepton flavor violation in decays of the Higgs boson with the ATLAS detector at the LHC is presented here. The analysis is performed in the H → lτ channel, where the leading lepton (l) can be either an electron or a muon, and the τ lepton decays into an opposite flavored lighter lepton or via the hadronic decay channel. Published results of this search are presented in this thesis based on a data sample of proton-proton collisions collected by the ATLAS detector corresponding to an integrated luminosity of 36 inverse-femtobarns (fb−1) at center-of-mass energy (√s) of 13 TeV during the 2015-2016 data-taking period. The analysis is found to be three times more sensitive than the previous analysis performed with 20 fb−1 of data collected at √s = 8 TeV during the 2012 data-taking period, and comparable to the one obtained by the CMS experiment with a similar-sized dataset at √s = 13 TeV during the 2015-2016 data-taking period. The direct search for lepton flavor violating decays of the Higgs boson obtained with the present analysis at the Large Hadron Collider is about twenty-five times lower than the indirect prediction. To complement my research goal of searching for new physics with lepton flavor violating signatures in final states containing the τ lepton, the generator level modeling of decays of the τ lepton decaying into Standard Model processes at the Belle II experiment at the world’s highest luminosity collider is also presented.