The front wheel drive Seville model name was retired in 2004, succeeded by an entirely new "STS" based on the rear wheel drive GM Sigma platform. The first Cadillac sedan to be offered with All wheel drive, it retained the Seville's high-performance Magnetic Ride Control suspension. The Cadillac STS was assembled at GM's Lansing Grand River facility in Lansing, Michigan along with the smaller CTS sedan.

Available engines were a 3.6 L High Feature LY7 V6 with 255 hp (190 kW) and 252 lb⋅ft (342 N⋅m) and the 4.6 L Northstar LH2 V8 which puts out 320 hp (240 kW) and 315 lb⋅ft (427 N⋅m) in the STS. All engine models feature dual overhead camshafts with variable valve timing. Remote ignition is standard.

Overall length was down 5" to 196.3", yet wheelbase grew by 4" to 116.4 in (2,957 mm), resulting in increased interior space. A heads-up display was optional, as was a 300-watt Bose stereo system with MP3 capability. Base pricing at launch ranged from US$40,575 for the V6 model to US$47,025 for the V8.