The 26-year-old will go straight into contention for Saturday’s trip to North Shields.
A former Rotherham United academy player, Cadman has also represented Stalybridge Celtic, Harrogate Town, Hyde United and Mickleover Sports.
On his move to the club, he said: “I’ve had a few weeks away from football, but after speaking with the gaffer and Danny South it was clear that this move to Ossett was a no-brainer.
"It’s time to start enjoying the game again.”
Sheepicorns manager Grant Black added: “James is a quality player who has excelled at the top levels of non-league for many years now.
“He was a big part of Scarborough’s promotion last year and he feels now is a good time for a new challenge.
“After many offers from the league above, all of which were financially way above us and some from managers he's worked with before, it shows how committed he is going to be with us.
“He's here for the right reasons, which is what we now want at this football club”.
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