Luongo and Gladwin have signed three-year deals with Chris Ramsey’s side as he looks to build a squad that can compete in the Sky Bet Championship next season.
Australia international Luongo, 22, joined Swindon on a three-year contract from Tottenham in August 2013 following an earlier loan spell with the Robins.
He has made 12 appearances for Australia and was named Most Valuable Player of the Tournament at this year’s Asian Cup.
Ramsey said of Luongo: “Mas is a player I know a lot about having played a part in his development at Spurs
“He brings quality on the ball; the ability to link up play all across the pitch; and his goals and assists record at club and international level speaks volumes for a creative midfielder.
“As with any young player, there are areas of his game that need improving, but knowing him as I do, I know he will embrace the learning curve of playing for us in the Championship. I am confident he will fluorish at Loftus Road.”
Gladwin, 22, has also established himself as a key member of the Swindon midfield after joining the club from Marlow in November 2013 following spells with a host of other non-league clubs.
Ramsey added: “Ben’s a fine addition for us and someone myself and Les (Ferdinand) have been monitoring for some time.
“I’m happy we’ve persuaded him to come here because there was a lot of interest from other clubs, some in the Premier League. He just wants to come in and play and he’ll get that opportunity with us.
“I’m looking forward to coaching him and working with a player I believe can only keep improving.”