Arthur, 27, has signed a two-year deal with the Mauve and Yellows after ending his stay at Elmina Sharks.
He becomes the latest addition to the squad following the capture of winger Zakaria Mumuni.
"Ben is a brilliant player and we're happy to have him here join the group," coach Samuel Boadu told medeamasc.com
"He is a top quality player who will be an exciting addition to our talented crop of players.
"Hopefully he can hit the ground running and contribute significantly to the Medeama project."
Benjamin Arthur said: "I am excited to be here as I open a new chapter in my career,"
"I want to thank coaches, officials, former colleagues and fans of Elmina Sharks for an amazing years at the club.
"They understand that a man must move on at some point in life. I am grateful for what we managed to do at Elmina.
"Now its time to shift focus on Medeama and contribute my bit to the success of this great team.
@MedeamaSC would like to announce the signing of midfielder Benjamin Arthur on a two-year deal.
Welcome to Tarkwa "Mido"!
— Medeama SC (@MedeamaSC) February 22, 2021
Benjamin won't be available for the Premier League match against Eleven Wonders at home on Wednesday but should be ready for the final game of the first round against Chelsea in Berekum.