Consumers expect the appropriate tenderness, juiciness, and taste, a well as sufficiently long shelf life from meat subjected to thermal processing. One of the methods used to achieve this effect is sous-vide (SV). However, the low temperatures used in this method may not be sufficient to ensure the safety of the meat product. In order to increase safety and reduce adverse sensory changes, we suggest marinating the meat in fermented dairy products (FDP). The aim of the study was to determine the impact of marinating meat in FDP (kefir, yogurt, buttermilk), marinating time (3–12 days), and SV temperature (60 or 80 °C) on the quality and safety of pork steaks. Marinating the meat increases the level of loss during cooking, but at the same time, has no effect on the chemical composition and activity of water. The acidity of steaks decreases with the time of marinating. A few days of meat marinating in buttermilk or yogurt slows down the fat oxidation reactions and reduces the content of oxidizing substances in meat. Meat marinated in FDP and SV cooked contains acceptable microbial values. Marinating in FDP, especially in yogurt or buttermilk, improves the quality and safety of SV-cooked pork steaks.