The development of new steels with high fatigue resistance is critical for various industries as it improves the longevity and reliability of structures and components subject to repeated loading. Bainitic steels have emerged as a promising option in this regard due to their unique microstructure and superior fatigue properties compared to conventional steels. Additionally, the re-use of steel products not only reduces waste and environmental impact, but also enhances the overall sustainability and cost-effectiveness of steel applications. To fully realize the potential of bainitic steels in engineering applications, it is crucial to understand the underlying fatigue mechanisms and how they vary among different types of bainitic steels. For this matter, microstructure, mechanical properties, and high-cycle fatigue properties of carbide-bearing bainite (CBB) and carbide-free bainite (CFB) were studied. Microstructural characterization was done via SEM and EBSD. In CBB, bainitic ferrite formed as primary phase, while cementite precipitated as secondary phase. In CFB, retained austenite (RA) and martensite-austenite (MA) islands were introduced as secondary phases due to Silicon (Si) addition. The low solubility of Si in cementite hinders cementite precipitation. This enables carbon diffusion from ferrite to austenite during phase transformation, which results in stabilization of the austenite. The mechanical properties of the CFB were superior compared to the CBB. It exhibited higher hardness, yield strength, tensile strength, and ductility. The metastable retained austenite in the CFB showed TRIP effect during deformation, which enhanced the mechanical properties. The high-cycle fatigue strength of both bainitic steels were determined via staircase method. Existence of the RA effectively improved the high-cycle fatigue properties of the CFB. During fatigue loading, the metastable RA transforms to martensite and delays the crack propagation by absorbing the energy that is necessary for the crack propagation. Additionally, determined fatigue strengths via staircase method were compared with a one specimen test, called increasing load test.