Canadian Formula 2 driver Nicholas Latifi will join Williams as a reserve driver in 2019.
Latifi joins the team from Force India, where he held the role of test and reserve driver this year. In his new role with Williams he will take part in six Friday practice sessions, one pre-season test and two in-season tests.
The 23-year-old scored one victory in F2 this year at the Spa-Francorchamps sprint race and finished the season ninth overall.
"I'm thrilled to be joining an iconic team like Williams as a Reserve Driver for 2019," he said. "It's a fantastic opportunity to continue my F1 development, and to build my on-track experience with more FP1 sessions and the rookie and Pirelli tests. As well as this, a big part of my role will be simulator driving and helping to support the development of the new car.
"I look forward to spending time in the factory at Grove, immersing myself within the team and assisting wherever I can. This is an amazing opportunity that I've been given and I'm excited to get started."
Claire Williams, deputy team principal, added: "I am delighted to confirm Nicholas Latifi as a Reserve Driver for the 2019 season. Nicholas has been racing successfully in the junior formula, he has the racing pedigree that we're looking for and he is incredibly intelligent and diligent.
"Nicholas will drive in FP1 sessions and at several tests next year. Along with this, he will undertake simulator work for the team. We are certain he will be a great fit for the team and we look forward to working with Nicholas next season."
Williams confirmed its 2019 driver line-up at the final race of the season in Abu Dhabi, with Robert Kubica due to race alongside F2 champion George Russell.