The second-generation Mercedes-Benz SLK (R171) launched at the Geneva Motor Show in March 2004. Its exterior styling drew heavy inspiration from Formula 1 racing cars and the SLR McLaren hypercar with a prominent front arrow nose. The chassis offered 46% higher torsional stiffness, while the updated Vario-Roof folded faster and occupied less boot space. The R171 introduced the Airscarf neck-level heating system integrated into the headrests.

Powertrains spanned from the 1.8-liter supercharged four-cylinder (SLK 200 Kompressor) to 3.0-liter and 3.5-liter V6 engines (SLK 280, SLK 350 producing up to 305 hp). Mercedes-AMG created the SLK 55 AMG, installing a naturally aspirated 5.4-liter V8 engine developing 360 hp mated to a 7G-Tronic transmission. A rare track-focused SLK 55 AMG Black Series with a fixed carbon-fiber roof made 400 hp. A 2008 refresh modified front bumper aerodynamics and introduced direct-steer variable steering.