  We propose that the LHC hints for a Higgs diphoton excess and the muon g-2
(g_mu-2) discrepancy between theory and experiment may be related by
vector-like "leptons" charged under both U(1)_Y hypercharge and a "dark"
U(1)_d. Quantum loops of such leptons can enhance the Higgs diphoton rate and
also generically lead to U(1)_Y - U(1)_d kinetic mixing. The induced coupling
of a light U(1)_d gauge boson Z_d to electric charge can naturally explain the
measured g_mu-2. We update Z_d mass and coupling constraints based on
comparison of the electron g-2 experiment and theory, and find that explaining
g_mu-2 while satisfying other constraints requires Z_d to have a mass ~ 20-100
MeV. We predict new Higgs decay channels gamma Z_d and Z_d Z_d, with rates
below the diphoton mode but potentially observable. The boosted Z_d -> e+e- in
these decays would mimic a promptly converted photon and could provide a
fraction of the apparent diphoton excess. More statistics or a closer
inspection of extant data may reveal such events.
