  The joint analysis of the Dispersion and Faraday Rotation Measure from
distant, polarised Fast Radio Bursts may be used to put constraints on the
origin and distribution of extragalactic magnetic fields on cosmological
scales. While the combination of Dispersion and Faraday Rotation Measure can in
principle give the average magnetic fields along the line-of-sight, in practice
this method must be used with care because it strongly depends on the assumed
magnetisation model on large cosmological scales. Our simulations show that the
observation of Rotation Measures with $\geq 1-10 ~\rm rad/m^2$ in $\sim 10^2$
Fast Radio Bursts will be able to discriminate between extreme scenarios for
the origin of cosmic magnetic fields, independent of the exact distribution of
sources with redshift. This represent a strong case for incoming (e.g. ALERT,
CHIME) and future (e.g. with the Square Kilometer Array) radio polarisation
surveys of the sky.
