The Williams FW35 was a Formula One racing car designed and built by the Williams team for use in the 2013 Formula One season. It was driven by Pastor Maldonado and 2011 GP3 Series champion Valtteri Bottas in his Formula One debut. The car was launched on 19 February at the Circuit de Catalunya in Barcelona, Spain, with the team using an interim version of the FW34 for the first test in Jerez de la Frontera. This was also the team's last season using a Renault engine before a new long term deal with Mercedes was activated for 2014.

After an impressive 2012, which saw the team pick up their first win since 2004 at the Spanish Grand Prix, 2013 was a massive disaster for the team, similar to 2011. The team was eliminated in Q1 mostly along with Marussia and Caterham, and failed to score a point until Hungary, when Maldonado finished 10th. Bottas, on the other hand, qualified an impressive third in Canada, but could only finish 14th, and he failed to score a point until Austin, when he finished 8th. The team finished 9th in the Constructors’ Championship, with 5 points, their equal-worst season.