Butler was one of the out of contract players at the end of the season but Roberto has moved quickly to sign him on a new deal – performance related as most of the current deals appear to be.
Butler was one of the consistent performers last season and was one of the regular names on the scoresheet after a disappointing first season following his move to South Wales.
And that form has been rewarded by the club.
"Tom has been a very consistent performer this season,'' explained Roberto on the club's official website. "He had his best campaign for the club last season and to have someone who can play on the left or right with the same effectiveness is a huge bonus and asset.
"Tom is desperate to return to the level (Premiership) he reached with Sunderland and I'm delighted he'll be trying to do that with Swansea City.
"He's a better and more mature player than when he first arrived at the club. He's extremely talented and full of skill – we've all seen it this season.
"I've no doubt that Tom is a player of Premiership standard and I'm delighted he's committed himself to the club.''