The South African midfielder spent four years at Goodison Park before opting to join Tottenham Hotspur in January 2011.
However, just one year later he returned to Merseyside on a six-month loan deal, which was concluded on Sunday afternoon.
While taking the time to praise the club's supporters, Pienaar refused to rule out the possibility of rejoining the Toffees on a permanent basis.
"The first time I left I didn't say goodbye, this time around it's a bit sad. I just want to say thanks for the support from day one. I really appreciate it," he told the club's official website.
"It means a lot to me, this club. Let's just see what will happen in the summer."
Pienaar scored four goals for David Moyes's side in 14 outings this season.