On March 15, 1781, Pierre Méchain discovered this object, M100, together with its apparent neighbors, M98 and M99. His friend, Charles Messier, obtained its position on April 13, 1781, and included it in his catalog, immediately before finishing the third, final published edition.

M100 is one of the brightest member galaxies of the Virgo Cluster of galaxies.

M100 is a spiral galaxy, like our Milky Way, and tilted nearly face-on as seen from earth. It is among the first spirals that have been discovered, and listed by Lord Rosse as one of 14 "spiral nebulae" discovered to 1850. The galaxy has two prominent arms of bright blue stars and several fainter arms. The blue stars in the arms are young hot and massive stars which formed recently from density perturbations caused by interactions with neighboring galaxies.

Despite its nearly perfect symmetric outline, this galaxy appears slightly asymmetric, as on the southern (lower) side of the nucleus more (or brighter) young stars have formed.

M100 is located in the spring constellation Coma Berenices and can be seen through a moderate-sized amateur telescope. Amateurs can see the central regions of this galaxy as faint elliptical patch of uneven texture in small telescopes, or even in good binoculars. Under good observing conditions, suggestions of the inner spiral arms can be glimpsed in telescopes starting at 4 inch aperture (refractor or unobstructed reflector).
Five supernovae have been observed in M100 so far.

It is quite faint in 8" telescope under moderate conditions. Core is bright but not to bright and it is sorrounded by large faint halo.