Pienaar, 30, spent four years at Goodison Park before leaving for Spurs in January 2011. He returned 12 months later on loan and will wear the number 22 jersey.
He played 14 games for Everton last term and scored four goals.
"I am happy to be here. It took a few weeks to sort out, but I am delighted to be back and excited to play for Everton," said Pienaar.
"There was no doubt in my mind that I would be back here. At the end of the season, I told the manager how I felt and I am happy now it is all done."