Boys in Green midfielder signed by Championship club following after contract expiry with Derby County
The 29-year-old central midfielder opted not to sign a new contract with former club Derby County at the end of last season and was a free agent.
Leeds United manager Neil Warnock was happy to have landed Green's signature.
"I've always thought he was the kind of player who can create goals as well as score them," said Warnock of Green. "I've seen him grow since his days at Doncaster, I'm delighted to get him."
Green made his debut for the Boys in Green against Paraguay in May 2010 and was a member of the Irish contingent that played at Euro 2012, making an appearance against Spain.