Under the 2022 rules, every team has to use two Friday sessions for a rookie driver over the course of the season.
It will be the first official appearance on track on a grand prix weekend for the Dutchman, who had his maiden outing in an F1 car with Mercedes in the young driver test in Abu Dhabi at the end of the 2020 season.
The Grove team says the Formula E champion "will aid the team's preparation work ahead of qualifying and the grand prix".
The timing of the arrival of de Vries at Williams is intriguing, as Mercedes is known to be keen to find a race seat for the former McLaren protege, and a source has confirmed that there have been talks with Williams about a 2023 seat.
Last week, an online rumour suggested that de Vries would replace Nicholas Latifi within this season, perhaps prompted by his appearance at the Williams factory for a seat fitting, but the team dismissed that.
"Firstly, I'd really like to thank Williams for the opportunity to run in FP1," said de Vries. "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 1 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."
Head of vehicle performance David Robson said a different driver could provide useful input to the team.
"We are looking forward to having Nyck de Vries in the car for FP1 as it is always good to work with a new driver and get a fresh opinion on the car's strengths and weaknesses," said Robson.
"Nyck's experience and professionalism will be crucial on Friday as he will complete some of the key engineering tests in FP1 before he hands the car back to Alex for FP2."
Williams sporting director Sven Smeets, who has responsibility for young driver programmes, noted: "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."
