The Morocco international, who had one year to run on his contract at Villa Park, departed Feyenoord for the Premier League in 2012.
But 29-year-old El Ahmadi says he always harboured an ambition to return to De Kuip.
"I've always said that I wanted to return to Feyenoord sometime," said El Ahmadi.
"That time has come. In my first period at this club Feyenoord was growing and that growth has continued in recent years.
"I'm really looking forward to playing in a full De Kuip again and sharing my experience with the other Feyenoord players. I'm also relishing teaming up again with [coach] Fred Rutten, who was very important for me at the start of my career at FC Twente."
Feyenoord technical director Martin van Geel added: "We’re happy that we are able to add this experienced player to the squad, which gives us more options in midfield.
"What’s more, El Ahmadi has successfully worked with Fred Rutten in the past, while he is obviously also used to playing for Feyenoord and at De Kuip."
El Ahmadi scored three goals in 51 appearances for Villa.
