Multiple theories beyond the Standard Model predict the existence of heavy Majorana or Dirac neutrinos. The ATLAS searches presented here focus on models in which these heavy neutral leptons are either produced together with a right-handed W gauge boson, via the Keung Senjanovic process, or with a heavy charged lepton from the same fermionic triplet, in the context of a type-III seesaw model. The searches focus on final states containing two leptons (of opposite signs or of same signs) and jets, using proton-proton collisions at \sqrt{s}= 13 TeV collected with the ATLAS detector at the LHC.