The Mercedes-Benz M273 is a V8 naturally aspirated gasoline engine that was produced from 2005 to 2010, designed as the successor to the M113 engine. It shares many design principles with the M272 V6, including an aluminum block and heads, DOHC configuration, four valves per cylinder, and continuous variable valve timing on both intake and exhaust camshafts. The M273 also features an internal balance shaft (similar to the M272) to reduce engine vibration. Available in displacements of 4.6 liters (M273 E46) and 5.5 liters (M273 E55), this engine was used in several high-end Mercedes-Benz models, including the S-Class (W221), E-Class (W211), CLS-Class (W219), and GL-Class (X164).

Functionally, the M273 was engineered to deliver refined yet powerful performance, offering strong torque throughout the rev range and a smooth, linear power curve typical of naturally aspirated V8s. It was intended to combine the performance expected from a V8 with modern efficiency and emissions compliance. However, like the M272, the M273 was also affected by a notable reliability issue in early models: balance shaft gear wear and problems with the intake manifold tumble flaps, which could trigger engine warning lights and require costly repairs. Despite these concerns, the M273 remains respected for its strong performance, smooth operation, and satisfying exhaust note, particularly when properly maintained and updated with revised components.