Just one day after Aitken announced that he had stepped down from his reserve and test role with Renault, the young British driver revealed that he had taken on a similar position at Williams.
As part of the deal, Aitken will attend all grands prix with Williams to work with the engineers, take part in one FP1, and will also conduct a full simulator programme.
Speaking about the opportunity, Aitken said: “It is a great honour to join ROKiT Williams Racing as their reserve driver for the 2020 season. Williams is a team with strong heritage, and continued longevity, and I’m looking forward to directly contributing to their development through my simulator and testing work.”
Deputy team principal Claire Williams added: “It is obvious from what Jack has achieved so far he is a young driver with a great career ahead of him and we believe he has the right credentials to reach the top in the sport.
“Jack has proved his ability in FIA Formula 2 and GP3 and we look forward to seeing what he can achieve as the team’s official reserve driver.”
Aitken had been a Renault junior since 2016, following on from his Formula Renault Eurocup title win the previous year. He finished fifth in GP3 with Arden in 2016, and then runner-up to George Russell one year later after a switch to ART Grand Prix.
Aitken took 11th in Formula 2 in 2018 after graduating with ART, while teammate - and current Williams F1 race driver - Russell won the title.
Last season Aitken switched to the Campos Racing's F2 squad and helped it move up the grid, finishing fifth in the championship while scoring three wins and four podiums.
Williams has a roster of young drivers on its books, with Dan Ticktum and Jamie Chadwick on board as development drivers, while Roy Nissany has an official test driver role.