The Williams FW43 is a Formula One car constructed by Williams to compete in the 2020 Formula One World Championship. The car was driven by Nicholas Latifi and George Russell, who were in their first and second year with the team respectively. Jack Aitken, Roy Nissany, Jamie Chadwick and Dan Ticktum acted as reserve and development drivers for the team.

One of these reserve drivers, Jack Aitken, made his Grand Prix debut in the FW43 at the 2020 Sakhir Grand Prix, replacing George Russell who was called up by Mercedes for the same event after Mercedes' regular driver, Lewis Hamilton, tested positive for coronavirus and was forced to miss the event as a result. Russell returned to Williams for the season finale in Abu Dhabi after Hamilton was cleared to race for Mercedes in that event with Aitken returning to reserve driver.

The car was designed by Doug McKiernan and Dave Wheater with new recruits David Worner and Jonathan Carter acting as Chief Designer and Deputy Chief Designer respectively. The car was planned to make its competitive debut at the 2020 Australian Grand Prix, but this was delayed when several races were postponed or cancelled in response to the COVID-19 pandemic. The FW43 made its debut at the 2020 Austrian Grand Prix.

The pandemic also prompted the delay of technical regulations that had been planned for introduction in 2021. Under an agreement reached between teams and the Fédération Internationale de l'Automobile, 2020-specification cars—including the FW43—saw their lifespan extended to compete in 2021. Williams introduced the FW43B for use in 2021.