The move, which is subject to international clearance, sees the left-back sign a three-year deal at Tynecastle.
The 24-year-old, who spent the last three years at Israeli club Ashdod, joined his new team-mates in training for the first time on Saturday morning.
Oshaniwa played in all of Nigeria’s matches at the 2014 World Cup in Brazil, including against Lionel Messi and Argentina.
Head coach Robbie Neilson told Hearts News: “I’m delighted to get Juwon here and signed up.
“It’s been a long process to get him here in Edinburgh, but he’s here now and he’s desperate to get started.
“He’s a top quality player and he’ll bring a lot of qualities to our squad. We’re all very happy with this move.”