Head, who helped establish Williams F1 with Frank Williams in 1977 and has since led the team's engineering department, will continue to be involved with the team's development of hybrid technologies.
Frank Williams said in a statement on www.williamsf1.com: "Patrick and I have been in partnership for 34 years. During that time, he has been the leader of the technical team that has won the majority of our race wins and championships.
"This is a remarkable legacy and one which will be treasured and definitely not forgotten.
"I will miss him very much, as I am sure his colleagues will, and he will always be welcome at Grove."
Williams F1 have won 113 Grands Prix and claimed nine Constructors' and seven Drivers' World Championships.