M. laevigata is a small fish, reaching a maximum standard length of 3.1 centimeters (1.2 in).[2] The mouth of the fish faces downward, with broad lips containing papilla.[5] The fish has three pairs of barbels. The maxillary barbels are on located on the upper jaw, and two pairs of mandibular barbels are on the lower jaw.[6] The front edges of the dorsal fins and the pectoral fins are hardened into stiff spines that can be locked into place.[6] The body shape is cylindrical along its entire length.[5]
M. laevigata can be distinguished from other members of the genus Microsynodontis by the structure of the pectoral spine, the shape of the caudal fin, and the length of the adipose fin. When viewed from above, the front edges of the pectoral spines appear smooth rather than serrated. The trailing edge of the caudal fin is straight, instead of forked or rounded. Only M. lamberti shares those characteristics. M. laevigata differs from M. lamberti by having an adipose fin that is about 33% to 35% of the standard length of the fish, instead of about 25% to 31% of the standard length.[3]