The midfielder joins the French Ligue 1 side after three seasons with Portuguese outside Rio Ave.
Wakaso, younger brother of Ghanaian international Mubarak Wakaso joins fellow Ghanaian Abdul Majeed Waris at the Club.
"I have heard a lot about FC Lorient by Pedrinho , In particular, and by Majeed Waris, who is a great friend.
“They told me good and I am happy today to arrive at the FCL. Playing in France was a real goal and being able to do it today is a great pleasure.
“With my new teammates we have a great challenge to keep the club in Ligue 1. We have the arguments to do it and I will do everything to reach it.
The 25-year-old misses out in Ghana’s 23-man squad for the Africa Cup of Nations tournament in Gabon.