Brisbane announced the deal overnight and Barbarouses will join the Brisbane squad for pre-season training at the start of May.
Wellington-born striker Barbarouses, who will turn 20 this month, has spent the past two seasons with rival A-League club Wellington Phoenix.
Barbarouses said the prospect of linking with coach Ange Postecoglou's squad was an exciting one.
"It's a time in my career where I have to get out of the comfort zone and really give myself a challenge," Barbarouses said.
"These next few years with Brisbane will be really crucial for my career leading into the most crucial years of the early 20s.
"I'm leaving my hometown club and I'm really excited for the challenge ahead with the Roar."
Postecoglou said he believed Barbarouses would be a perfect fit for the squad he is building.
"I think he fits in with the style of football we want to play," Postecoglou said.
"He's quick, exciting at an age where he really wants to break through and make a name for himself.
"We don't have his type of striker at the club, when you have a look at what we have with Reinaldo and Sergio (van Dijk), they are big strong strikers.
"Costa will give us that variety and we've already shown that if young players are good enough we'll play them."
Barbarouses said leaving his hometown club would be difficult, but the keen interest shown by the Roar to secure his services had persuaded him it was the right decision.
Despite limited game time this season, the young striker scored against Sydney in November with a volley over Clint Bolton and has two assists to his credit.
Barbarouses has represented New Zealand at under-17, where he captained his country at the 2007 World Cup tournament in Korea, under-20 and under-23 levels.
In November 2008 he made his senior debut for the All Whites against Fiji during the World Cup Qualifying process.
Barbarouses' flight highlights a major hurdle the Phoenix have in developing young New Zealanders without the presence of a reserve team.
