Teh 22 year old had just signed a new deal with the Toon, but immediately comes out on loan to the Millers.
Rotherham boss Paul Warne has beat off a number of clubs in the Championship to secure the 6ft 1" striker who impressed on loan with Accrington Stanley last season.
"We went and visited a club to sell the dream really and to present to them how we play and how it would help us and their player if he came on board." Warne told the Star.
Barlaser should feature in tomorrow's game against Parkgate at Roundwood - KO 1pm
"I think most players and agents in this league will think we're a team that will be in the top half of the table. It's a good place to come and play.
"It's full of great people and in recent years we've had success in kicking players' careers on. It isn't a hard club to sell at the moment. I think our reputation is really good." Warne added.