  Strongly supercooled first order phase transitions (FOPTs) can produce
primordial black hole (PBH) dark matter (DM) along with observable
gravitational waves (GWs) from bubble collisions. Such FOPTs may also produce
coherent magnetic fields generated by bubble collisions and by turbulence in
the primordial plasma. Here we find that the requirement for PBH DM can produce
large primordial magnetic fields which subsequently yield intergalactic
magnetic fields in the present universe (with magnitude $\lesssim 20$ pG across
coherence length scales of $\simeq 0.001$-$0.01$ Mpc, assuming maximally
helical magnetic fields) that easily exceed lower bounds from blazar
observations. We follow a largely model independent approach and highlight the
possibility of producing DM and observable multi-messenger magnetic fields and
GW signals visible in next generation experiments.
