NGC 3109 is a small barred Magellanic type spiral or irregular galaxy around 4.35 Mly away in the direction of the constellation of Hydra.

Based on the D25.5 isophote at the B-band with an angular diameter of 1,980 arcseconds, it has an isophotal diameter approximately 12.80 kiloparsecs (41,700 light-years) across, slightly larger than the Large Magellanic Cloud but smaller than the Triangulum Galaxy.

[9] From measurements of the neutral atomic hydrogen in the galaxy, it has been found that the disk of NGC 3109 is warped.

[11] Based on spectroscopy of blue supergiants in NGC 3109, it is known that the galaxy has a low metallicity, similar to that to the Small Magellanic Cloud.

[13] Although no supernovae have been observed in NGC 3109 yet, a luminous blue variable, designated AT 2018akx (type LBV, mag.