Arthur, 23, hails from Ghana and has recently been on the books of Portuguese side AD Fafe, in the third tier.
The central midfielder had spells with Gil Vicente, Ars Marthino and the U-19’s team of Porto as well.
The Citizens have already acquired the services of Michele Sansone from Sliema, Christian Gauci of San Ġwann and Birkirkara duo Caio Prado and Alessandro Guarnone.