[7] In Danish astronomer J. L. E. Dreyer's New General Catalogue of Nebulae and Clusters of Stars it was described as: considerably bright, large, very little extended, gradually pretty much brighter middle, and partially resolved.

[5] In the Third Reference Catalogue of Bright Galaxies, NGC 7421 was assigned a morphological classification of SB(rs)bc, which indicates a barred spiral galaxy (SB) with a transitional ring structure (rs) and moderately wound spiral arms (bc).

It displays an asymmetric morphology, which shows up in a lopsided optical appearance and in the distribution of CO and neutral hydrogen atoms.

The gas fraction and star formation rate is significantly lower than normal, suggesting an interaction with the external environment.

Radio mapping of neutral hydrogen by the ATCA displays an extended wake to the north and south of the galaxy, supporting this hypothesis.