The importance of lipid molecules present at the level of cell membranes is already well known. They can act as secondary messengers, participating in signal transduction processes that regulate various organ functions; furthermore, their nature significantly influences cellular properties and functions. Recent studies have seen how the lipid composition of cell membranes is connected to the animal lifespan and the onset of several pathological conditions. While numerous studies have been conducted aimed at characterizing the membrane lipidomic profile in the human field, in the animal field, especially in pets, the number of studies is very limited. In recent years, preliminary analyses have been conducted to provide initial information on the composition of membrane fatty acids in healthy pets and those with chronic enteropathy. The results of these studies are very interesting as they highlight differences in fatty acid composition between the two groups of animals. Obviously, a greater number of works is needed to obtain more reliable results and to analyze how the membrane lipid composition can vary in different breeds and sizes of dogs and cats in an attempt to understand the mechanisms underlying it. The present review is divided into three main parts: the first one examines the close influence of fatty acids on membrane properties/functions, the second one presents the main lipidomic analyses conducted so far on companion animals, and the third and final part summarizes the latest works on the link between membrane lipid profiles and animal lifespans, also focusing on dietary and non-dietary strategies able to influence it. Membrane lipidomics allows us to obtain a concrete overview of an animal's metabolism and nutrition; furthermore, lipid alterations could be used as biomarkers for the early diagnosis of pathologies. This represents an innovative tool in the veterinary field to monitor the metabolic/health status of animals.