It was discovered by Charles Messier in 1764 and included in his list of comet-like objects.

[8] From the perspective of Earth, M18 is situated between the Omega Nebula (M17) and the Small Sagittarius Star Cloud (M24).

[10] It has a Trumpler class of II 3 p.[4] The cluster is 33[6] million years old with an estimated mass of 188 M☉.

[11] The brightest component (lucida), designated HD 168352, is a B-type giant star with a class of B2 III and a visual magnitude of 8.65.

It passes vertically through the galactic plane once every 27.4 million years, ranging no more than 80 pc above or below.