​Billy Mitchell came through the youth academy at Millwall [Getty Images]Sheffield Wednesday have signed midfielder Billy Mitchell on a free transfer from Millwall.The 25-year-old has signed a three-year deal at Hillsborough and becomes the club’s eighth signing of the summer window.He will be reunited with fellow ex-Millwall midfielder Barry Bannan who re-joined the Owls earlier this month.Mitchell made 30 Championship appearances for Millwall last season as the Lions were eventually beaten in the play-off semi-finals by Hull City.In total, the midfielder played 196 times for Millwall since making his debut on the final day of the 2018-19 season.”I’m very excited, this is a massive club, massive opportunity,” Mitchell told Wednesday’s website.”We all know Sheffield Wednesday doesn’t belong in League One and I, along with the rest of the boys, am going to make it our sole mission to get promoted.”Latest Sheffield Wednesday news, analysis and fan viewsListen to Sheffield Wednesday content on BBC SoundsAll done deals in July 2026