The Gateshead-born 23-year-old, who has represented both England an Turkey at youth level, had been with Newcastle for 14 years after joining the Little Benton Academy from Darlington in 2006.
He progressed through the ranks to make his first team debut in an FA Cup win against Birmingham in January 2017, making further cup appearances against Oxford United and Nottingham Forest before heading out on loan to Crewe Alexandra, then Accrington Stanley.
Last season, he joined Rotherham on a season-long loan and was a key player as Paul Warne's side won promotion from League One. His performances for the Millers earned him a fourth appearance for Newcastle in last month's Carabao Cup win against Blackburn Rovers - 1,119 days after his third - and another in the 7-0 win at Morecambe in the same competition.
However, with the deadline looming for Newcastle United to name their 25-man squad for the 2020/21 Premier League season, Steve Bruce has decided to allow Barlaser to rejoin the Millers, this time on a permanent basis. He has signed a three-year contract at the New York Stadium.
"I wish Dan the very, very best of luck," said the Magpies' head coach. "He had a wonderful loan spell last year. He's got to an age where I think he needs to play, and I hope he goes and has a wonderful career.
"He's been with us since he was nine years old and I wish him the best of luck."