The globular cluster M3 was the first 'original' discovery by Charles Messier, on May 3, 1764. This contrasts to the 'accidental' discoveries of M1 and M2, which occured a few years earlier. It was this discovery that led Messier to start a systematic search for these 'fuzzy' objects that resembled comets, but weren't, since they detracted from Messier goal of comet-finding. By the end of 1764, Messier had cataloged Messier objects M3 through M40.
William Herschel (discoverer of Uranus) was the first to resolve M3 into stars and recognize it as a cluster around 1784.
E. C. Pickering, in 1889, discovered the first variable star in M3. By 1978, 212 had been found, more than any other known object. M3 is also surprisingly blue for a globular cluster, with its spectrum being rated from F2 to F7. This seems to be due to the rather large number of blue stragglers within M3.
With a magnitude of 6.2, M3 is barely visible with the naked eye only under the best viewing conditions. However, binoculars or a small telescope will easily bring the object into view. To find M3, extend the line from Gamma Comae Berenices near the Comae Berenices Cluster over Beta Comae by about 2/3 and look slightly north. M3 is about 6° NNE of Beta Comae.