Antonio, 22, became a fans' favourite at Hillsborough during a loan spell last season when he netted five goals in 14 games.
He also helped them clinch promotion back to the Championship - sparking Owls boss Dave Jones to sign the winger for around £600,000 this week on a four-year contract.
And it seems Jones has big plans for the former Tooting & Mitcham player.
"We had to wait a while to get this one done and had to show a lot of patience," said Jones.
"The boy made it obvious he wanted to come to us but there were a few hurdles to clear.
"A lot of hard work has gone into this one and I'm pleased for everyone involved.
"He won't be required to settle in because of when he was here on loan. That is a big bonus and will work in our favour.
"I've every confidence in him and so does everybody else. I think people forget that he is still a prospect and that's because of the impact he had here last season."
Antonio joined Royals in 2008 but made only four starts and 24 substitute's appearances, scoring once.
He enjoyed previous loan spells with Cheltenham, Colchester and Southampton.
His chances of first-team football with Reading appeared limited this season with wingers Jobi McAnuff, Jimmy Kebe, Garath McCleary and Hal Robson-Kanu now standing in his way.
Royals' director of football Nick Hammond said: "It's a good move for Michail, he's going to a big club with good people - and he did a great job for them last year."