Buckley, 25, who has been training with Leeds this week, has finalised an emergency loan deal that will keep him at Elland Road until January 2 and could make his debut in the home game against Birmingham on Saturday.
Buckley told the club's official website: "I wanted to go out and get some games at a big club and Leeds was the perfect opportunity for me to do that.
"There was interest in the summer but after the transfer window closed Leeds were still there and they showed they were keen to get me.
"I was keen to come here and eventually it got sorted out, which I was pleased about."
Oldham-born Buckley started out at Rochdale and joined Watford for an undisclosed fee in 2010 before Brighton signed him for £1m in the summer of 2011.
Sunderland paid £2.5m to take Buckley to Wearside in August 2014 and although he made a total of 25 appearances for them in his first season, he has yet to feature for the Black Cats in the current campaign.