Symonds joined in 2013 and helped lead the team to consecutive third-place finishes in the constructors’ championship before it slipped to fifth place this year.
Coming to the end of his three-year contract, Williams has now confirmed the 63-year-old will leave the team on December 31.
Deputy team principal Claire Williams praised Symonds for the impact he has had on the team since his arrival.
“Pat has been a tremendous asset to this team over the past three years,” Williams said. “Pat’s appointment was the start of a major restructuring exercise, and he has been pivotal in reshaping Williams into what is a much stronger racing team today.
“I would like to thank him for all of his hard work and commitment during that time. We now look to the future and will be announcing details regarding the team’s technical leadership in due course.”
Williams has been linked with a move for Mercedes executive director [technical] Paddy Lowe, who is believed to be moving closer to a senior technical role at Grove.