He will be eligible to play for Sheffield on Sunday when they host Aston Villa in their opening in their opening league game and it has also been confirmed he will be wearing the number 38 on his shirt.
Biggest flop for the club
The 26-year-old struggled to make any sort of splash impact at the Stadium of Light following a £2.5 million move from Brighton and Hove Albion back in 2014, while his time on Wearside was short lived after spending the the majority of last season on loan at Leeds United and Birmingham City.
He was sent out on loan to Leeds last Autumn where he only played four games for the Whites before returning back to Sunderland and then heading back out to Birmingham City again on loan 'til the end of the season.
Buckley made his name with Brighton scoring 19 goals in 64 league game starts before following former manager Gus Poyet to the North East.
He didn’t feature at all for the Black Cats last season and didn’t join the team on tour in France for their pre-season games over the summer off-season.
He also made 24 appearances during his first season, but it was mostly as a sub from the bench. With a year left on his contract at Sunderland, it was always inevitable that he was likely to leave during this summer.
The Hillsborough club narrowly missed out on promotion to the Premier League last season losing out to Hull City in the Championship Play-Off final but now the Owls have made the move for Buckley he will be linking back up with another former Sunderland team-mate Steven Fletcher who also signed for the club earlier in the summer.