Di Maria, 35, played for the Portuguese club between 2007-2010 when he first moved to Europe from Rosario in his native Argentina.
He spent last season with Italian side Juventus after seven years with French giants Paris St-Germain.
"Welcome home, Di Maria," said the club in a video announcing his move, which is reportedly a one-year deal.
Di Maria won the Portuguese league and cup double in his last season with Benfica before moving to Real Madrid.
He will join close friend and compatriot Nicolas Otamendi, with whom he won the World Cup in Qatar last year.
We need your consent to load the translations
We use a third-party service to translate the website content that may collect data about your activity. Please review the details in the privacy policy and accept the service to view the translations.