Long-time McLaren Formula 1 test driver and Mercedes DTM frontrunner Gary Paffett will join Williams as a simulator driver for 2016.
Paffett, the 1999 McLaren Autosport BRDC Award winner and 2005 DTM champion, conducted extensive F1 testing with McLaren during a 13-year association with the team that ended in 2013.
Williams deputy team principal Claire Williams said: "We're delighted to have someone with Gary's experience join us at Williams.
"He is a highly professional racing driver and his level of testing knowledge, and ability to analyse data, will significantly help to drive forward development of the FW38 throughout the season."
Although Mercedes has yet to announce its 2016 DTM line-up, Paffett is expected to stay on.
Paffett said he was pleased to be joining a team with Williams's "great pedigree and history in Formula 1."