The 24-year-old German full-back arrives from Premiership rivals Hamilton, where he made seven appearances after joining in October.
A former Arsenal trainee, Sowah spent time at Portsmouth, Hamburger SV, Millwall and Danish side FC Vestjaelland before his switch to the Accies on a short-term deal which expired on 1 January.
Sowah told the club’s website that: “My favourite position is left-back but I can also play in the middle or out on the wing. But left-back is where I prefer to play and I will do my very best to help the team succeed.
“I feel right at home in Scotland. I’ve played in England before and I love the passion for the game over here.”