  The heavy element abundance profiles in galaxies place stringent constraint
on galaxy growth and assembly history. Low-redshift galaxies generally have a
negative metallicity gradient in their gas and stars. Such gradients are
thought to be a natural manifestation of galaxy inside-out formation. As the
Milky Way is currently the only spiral galaxy in which we can measure
temporally-resolved chemical abundances, it enables unique insights into the
origin of metallicity gradients and their correlation with the growth history
of galaxies. However, until now, these unique abundance profiles had not been
translated into the integrated-light measurements needed to seamlessly compare
with the general galaxy population. Here we report the first measurement of the
light-weighted, integrated stellar metallicity profile of our Galaxy. We find
that the integrated metallicity profile of the Milky Way has a '$\wedge$'-shape
broken metallicity profile, with a mildly positive gradient inside a
Galactocentric radius of 7 kpc and a steep negative gradient outside. This
metallicity profile appears unusual when compared to Milky Way-mass
star-forming galaxies observed in the MaNGA survey and simulated in the TNG50
cosmological simulation. The analysis of the TNG50 simulated galaxies suggests
that the Milky Way's positive inner gradient may be due to an inside-out
quenching process. The steep negative gradient in the outer disc, however, is
challenging to explain in the simulations. Our results suggest the Milky Way
may not be a typical spiral galaxy for its mass regarding metallicity
distribution and thus offers insight into the variety of galaxy enrichment
processes.
