"I'm honoured to be asked to play a role in returning the team to its rightful place at the pinnacle of Formula One,"
He was a fixture at the team that is now Lotus, but which has gone through a series of guises as Toleman, Benetton and Renault from its inception in the early 1980s until 2009 and he built a reputation as one of F1's foremost engineers.
Symonds returned to F1 as a consultant with Marussia last year and was this year allowed to attend races in a formal capacity again for the first time since the ban.
"Williams is a team steeped in success and engineering excellence," he added.
Williams Formula One team
Debut season: 1975
Constructors' world championships: Nine
Drivers world championships: Seven
Last team world title: 1997
Pole positions: 127
Fastest laps: 131
"Sir Frank, chief executive Mike O'Driscoll and deputy team principal Claire Williams have put in place the foundations for success and I'm immensely excited to begin this new challenge."
BBC Sport understands these are the first of a series of changes planned at Williams in the coming months.
Williams Team Founder and Team Principal Sir Frank Williams said: "I'm delighted that Pat is joining the team.
"His technical capabilities and sporting successes speak for themselves and I'm sure that his knowledge and leadership will contribute considerably to the success that all of us at Williams are working hard to achieve."
O'Driscoll added: "Our commitment to return Williams to winning ways is absolute and this appointment is yet more evidence of our collective desire to return the team to the position it deserves."
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.