Monopoles are inevitable predictions of GUT theories. They are produced during phase transitions in the early universe, but mechanisms like the Schwinger effect in strong magnetic fields could give relevant contributions to the monopole number density. I show that from the detection of intergalactic magnetic fields of primordial origin, we can infer additional bounds on the magnetic monopole flux. I also discuss the implications of these bounds for minicharged monopoles, magnetic black holes, and monopole pair production in primordial magnetic fields.