It is positioned in the southern part of the constellation to the southwest of Eta Ophiuchi, and lies atop a dark cloud of dust designated Barnard 64.

[5][8] The cluster was discovered by French astronomer Charles Messier on June 3, 1764, who described it as a "nebula without stars".

[9] In 1783, English astronomer William Herschel was able to use his reflector to resolve individual stars within the cluster.

The brightest individual stars in M9 are of apparent magnitude 13.5, making them visible in moderately sized telescopes.

Based upon the periods of the RR Lyr variables, this cluster is classified as an Oosterhoff type II globular, which precludes an extra-galactic origin.