Israeli driver Roy Nissany will have a day of pre-season testing and take part in three Friday practice sessions for Williams this season.
Nissany, 26, ended up 19th in Formula Two last year after finishing 22nd in 2019 but Williams, who changed ownership last August, said he would continue in the role of official test driver.
He took part in free practice in the Spanish, Italian and Bahrain Grands Prix last year as well as the post-season test in Abu Dhabi.
"As a team, we were very happy with the contributions Roy made both through his work on-track and in the simulator at Grove, which all aided the lap time gains we were able to make with the FW43," team boss Simon Roberts said in a statement.
The former champions failed to score a point last year, finishing last overall. The season begins in Bahrain on March 28.