Osman was one of six trialists boss Alan Archibald cast his eye over during the 1-1 draw with Dumbarton on Saturday and has now been handed a deal at Firhill to become the second new arrival of the summer following the capture of Ryan Stevenson last month.
The 27-year-old is a free agent after leaving Crewe Alexandra at the end of last season and has previous experience of the Scottish top flight having turned out for 18 times for Gretna during the 2007/08 SPL campaign.
After leaving Raydale Park, Osman made over 100 appearances for Northampton Town before joining Corfu-based Kerkyra.
With Osman and Stevenson now on board, Archibald is likely to focus his attentions on defensive reinforcements ahead of the new Premiership campaign, with a left-back and centre-back top of his shopping list.
Former Hearts and Kilmarnock defender Darren Barr also featured against the Sons on Saturday while full-backs Matt Parsons and Jordan Mustoe were given a half each as they look to win a deal with the Jags.