The 22-year-old, who was tipped by many as the next Black Stars goalkeeper following his heroics with Ghana U20 side at the 2013 Fifa World Youth Championship, became a benchwarmer at Kotoko last season, losing his position to Ernest Sowah and Felix Annan. He played just three league games and eight in all competitions.
"I have agreed to join Medeama ahead of the new campaign. Things have not been good for me in recent months but all is not lost. I have to gather courage and face what the world has in stock for me," Antwi told Goal.
"Last season was my worst in the Ghana Premier League because I was in post for only three games out of 30 and it really affected my chances in the national team. I decided to move from Kotoko and face different challenges. Medeama will be the best place for me because I believe I will have the opportunity to play every weekend and regain my lost form."
He added: "My target is to hit top form very soon and challenge for the Black Stars goalkeeping position. I was very close to achieving that until I had the setback at Kotoko. The current third choice goalkeeper of the Black Stars was the second option to me during the U20 World Cup in 2013 so it means I am lacking behind but not entirely out of the equation. I can still be who I was few years back through hard work and determination."
The Ghana Premier League will commence on February 4.