  The discovery potential of both singlet and doublet vector-like leptons
(VLLs) at the Large Hadron Collider (LHC) as well as at the not-so-far future
muon and electron machines is explored. The focus is on a single production
channel for LHC direct searches while double production signatures are proposed
for the leptonic colliders. A Deep Learning algorithm to determine the
discovery (or exclusion) statistical significance at the LHC is employed. While
doublet VLLs can be probed up to masses of 1 TeV, their singlet counterparts
have very low cross sections and can hardly be tested beyond a few hundreds of
GeV at the LHC. This motivates a physics-case analysis in the context of
leptonic colliders where one obtains larger cross sections in VLL double
production channels, allowing to probe higher mass regimes otherwise
inaccessible even to the LHC high-luminosity upgrade.
