The 23-year-old defender has become the latest addition to Portuguese champions after successful medicals.
Sanusi caught the eye following his impressive showing for Santa Clara after scoring one goal in 24 league appearances in the Portuguese Primeira Liga last season.
Porto beat off strong competition from Greek club Olympiacos to sign the left-back.
“I will give everything on the field, for the fans and for everyone at the club,” Sanusi told the club’s official website.
“I’m really happy to be a FC Porto player. I don’t even know how to explain it, but I’m very, very happy to be wearing this shirt. ”
“I hope to do a good job and help the team. This season we will win everything. ”
“The club and the fans can expect everything from me. I received many messages from FC Porto fans and that made me very happy. ”
“I haven’t said anything to him yet, but I’m sure we’ll talk a lot. From now on I will be trained by him, so we will talk a lot, for sure. I am very motivated to start working. ”
Sanusi will join Super Eagles defender Chidozie Awaziem, who was on loan to Spanish side Leganes in the 2019-20 campaign, at the club.
The Nigerian has previously played for Portuguese club Gil Vicente and Mirandela could make his debut for Porto when they take on Sporting Braga in their next league game on September 20.