The Israeli driver currently competes in F2 with Trident, having previously competed in the series with Campos Racing in 2018.
Nissany previously tested for the team during last year's post-season tests in Abu Dhabi for the team and is a development driver with the team alongside fellow F2 drivers Jack Aitken and Dan Ticktum, as well as W Series champion Jamie Chadwick.
"I am very keen to get in the car in Barcelona," Nissany said.
"Driving an FP1 for the first time is a huge milestone for every driver, yet for me, it is also a national achievement to be carrying the Israeli flag.
"I have thoroughly been preparing for it with the team and I believe we can get great value out of it."
The FW43 will also run logos of Israel Start-Up Nation, which is currently funded by Canadian billionaire Sylvan Adams, who is currently backing Nissany's racing career.
Williams head of vehicle performance Dave Robson confirmed the intention for Nissany to drive for the team at this weekend's Grand Prix in Barcelona.
"Roy Nissany will drive George's car during FP1 at this event," Robson commented.
"We spent time with Roy in Abu Dhabi at the end of last year and we know that he will immediately be up to speed and contributing to the important test plan on Friday.
"We continue to push the FW43 hard and this return to Barcelona is an opportunity to explore again the higher downforce set-ups at a circuit that we know well."
Bahrain International Circuit - Winter testing