Reigning Formula E champion Nyck de Vries will drive for Williams during the first practice session for this weekend's Spanish Grand Prix.
De Vries is a Mercedes Formula E driver and one of the Mercedes F1 team's reserve drivers, as well as the 2019 Formula 2 champion.
F1's regulations this year require teams to run "young" drivers in at least two Friday practice sessions over the course of the season.
De Vries, who is 27, qualifies as a young driver because he has not raced in F1.
"Firstly, I'd really like to thank Williams for the opportunity to run in FP1," he said. "It's great for me to get to know the team and drive the FW44, and also to get myself out on track during a Formula One weekend.
"Preparation for the test is going well so far and the team have been incredibly supportive of me. I'm very much looking forward to the whole experience in Spain now."
Sven Smeets, Williams sporting director, added: "I'm looking forward to seeing Nyck join the team for FP1 at the Spanish Grand Prix. As he is a very talented and experienced driver I have no doubt that he'll maximise his time in the FW44 and deliver a strong, capable performance for the team."
De Vries will drive Alex Albon's car during the session before Albon returns to the cockpit for second practice and the rest of the weekend.