Barkley, who made his debut for the Toffees against QPR at the beginning of last season aged 17 and went on to make another five league appearances for David Moyes' side, has this campaign only made one appearance in the victory over Leyton Orient in the League Cup.
Wednesday manager Dave Jones is delighted to have signed Barkley on a short-term deal, and he believes it as big a coup as his capture of Barcelona striker Rodri on a season long loan.
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"We have been chasing Ross for some time and I'm really pleased to have him on board," Wednesday manager Dave Jones told the club's official website.
"This is as big as the Rodri signing for me because this lad is a real quality player. He's energetic, good in the air and a box to box player who can score a goal."Barkley will wear the No.24 shirt and is available for selection ahead of Wednesday's game against Brighton on Friday evening.