The Williams FW10 was the Formula One car built and raced by the Williams team for the 1985 Formula One season. The team introduced an upgraded version of the car dubbed the FW10B late in the season.

1985 marked Williams' second full season with Honda turbo power. 1984 had been difficult, as the FW09 struggled to cope with the enormous power and brutal torque curve, leading to handling problems which afflicted drivers Keke Rosberg and Jacques Laffite throughout the season. Technical Director Patrick Head thus decided to make the FW10 stiffer by making the monocoque entirely from carbon composite, rather than the aluminium honeycomb construction of previous years- the first Williams F1 car ever to be made predominantly of this material. This construction technique had been pioneered by the McLaren team with their MP4/1 in 1981, and was in the process of being adopted by the other teams for its combination of exceptional stiffness and lightness. In total, nine FW10 tubs were built; one was sent to Japan for Honda test driver Satoru Nakajima to drive, and one was a prototype to test the construction process.

During the 1985 season, two were written off in accidents: the first when Nigel Mansell went head-on into a barrier at Detroit, the second when he crashed heavily at Paul Ricard due to tyre blowout at over 200 mph (322 km/h), unwittingly setting the record for the highest speed crash in Formula One. The Honda engine proved to be extremely powerful, if not as reliable as the championship-winning TAG-Porsche turbo engine in Alain Prost's McLaren MP4/2B, with Head claiming around 1000–1250 bhp in qualifying, and up to 900 bhp (670 kW) in race configuration.

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