  The physical processes that establish the morphological evolution and the
structural diversity of galaxies are key unknowns in extragalactic
astrophysics. Here we report the finding of the morphologically-mature galaxy
JADES-GS+53.18343-27.79097, which existed within the first 700 million years of
the Universe's history. This star-forming galaxy with a stellar mass of
$10^{8.6}$ solar masses consists of three components, a highly-compact core
with a half-light radius of 144 pc, a strongly star-forming disc with a radius
of 468 pc, and a star-forming clump, which all show distinctive star-formation
histories. The central stellar mass density of this galaxy is within a factor
of two of the most massive present-day ellipticals, while being globally 1000
times less massive. The radial profile of the specific star-formation rate is
strongly rising toward the outskirts. This evidence strongly suggests the first
detection of inside-out growth of a galaxy as a proto-bulge and a star-forming
disc in the Epoch of Reionization.
