The Higgs boson, discovered in 2012 at the LHC, is at the origin of the electroweak symmetry breaking within the Standard Model (SM). Despite extensive studies on the Higgs properties, the Higgs self-coupling remains unexplored. This parameter is a key factor in determining the Higgs potential and the stability of the universe’s vacuum. Studying Higgs pair production is the only direct method for measuring this self-coupling, which will give crucial insights into the universe’s fundamental structure and the nature of the electroweak phase transition after the Big Bang. Di-Higgs production is predicted to have a very small cross-section within the SM. Among possible detection channels, the multilepton final state is promising due to its unique kinematic signature, though challenging due the need for precise lepton identification and advanced signal separation techniques using machine learning. This PhD project focuses on searching for di-Higgs production in the multilepton channel with 13.6 TeV ATLAS data, taking advantages from the increased data and energy in Run 3 and aiming to approach SM sensitivity.