In this role, which is focussed on augmenting car performance, Spagnolo will concentrate on understanding the Grove outfit's competitors' strengths and identifying areas of performance which require prioritisation of resources.
The team admits that in view of his previous role at Ferrari, his considerable experience will be brought to bear in guiding the restructured Tyre Performance Group to better understand and exploit both theoretical and practical aspects of tyre performance.
Spagnolo held various roles with Ferrari, including Race and Performance Engineer to Kimi Raikkonen and Fernando Alonso respectively. He has been with Ferrari since 2005, during which time it won two Constructors' titles, in 2007 and '08, and the '07 Drivers' title with Raikkonen.
According to the team, his experience and expertise will be a valuable addition to the Operations Group where he will report in to Head of Performance Engineering, Rob Smedley.
"Williams is determined to continue the positive momentum it has had since 2014 and, with new additions to the team, hopes to become even stronger," said Pat Symonds, Williams Chief Technical Officer.
"We are constantly seeing ways to improve our performance and trackside operations and believe Antonio will make a valuable contribution to this process. As a team, we will do our utmost to achieve our on-track ambitions and secure strong positions in the Constructors' Championship this season, and beyond."