Recruited from Temora, New South Wales, Breust played both rugby league and Australian rules football as a junior but turned his focus to Australian rules from age 14. Breust played football and basketball with Isaac Smith in Temora before the latter moved to Wagga Wagga when he was 13, with both ending up at Hawthorn where they played together in the 2013 AFL Grand Final.
As stated on the NSW AFL website, 'Before being drafted at the age of 18, Breust played with many current stars of the game as a member of the NSW/ACT Rams side that took out the Division 2 title at the NAB AFL Under-18 National Championships in 2008.'
"Craig Bird was my captain and I played with Taylor Walker, Dean Terlich and guys like that," he said.
He was drafted by Hawthorn with selection 47 in the 2009 AFL Rookie Draft in December 2008. Breust fractured his left tibia during 2008, but after recovering from that injury he received an invitation to trial with the Hawks and was then selected in the draft.
In Round 8 of the 2011 AFL season, Breust made his debut against St Kilda after performing well for Hawthorn's affiliate side in the Victorian Football League, Box Hill. He kicked 2 goals after coming on as a substitute. In Round 15 after a 2-goal, 16-possession game against Collingwood, he was nominated for the 2011 AFL Rising Star Award.
Breust improved more during the 2012 AFL season, particularly with his five goal effort in Hawthorn's eight goal win over Collingwood. He played predominantly as a forward, but had short bursts in the midfield throughout the year. Breust played in Hawthorn's losing Grand Final team. At the end of the year, he placed fourth in the Peter Crimmins Medal behind winner Sam Mitchell.
Breust's cousin Trent Barrett represented Australia and New South Wales in rugby league and won the Dally M Medal for best and fairest player in the National Rugby League in 2000.
In 2013, Breust kicked a goal in the last quarter of the AFL Grand Final against the Fremantle Dockers to win his first AFL Premiership.
In 2014, Bruest began a streak of 29 consecutive goals without scoring a behind, tying with the record set by Tony Lockett in the 1995 season. The streak began during the last quarter of Round 5 against the Geelong Cats and was broken in Round 17 against the Adelaide Crows.
In Round 21, 2017, Bruest kicked his 300th career goal in a 27 point victory over North Melbourne.Statistics are correct to the end of 2017. Team3× AFL Premiership: 2013, 2014, 20152× McClelland Trophy: 2012, 2013IndividualAll-Australian: 20142× 22under22 team: 2012, 20132× Australian Representative Honours in International Rules Football: 2014, 2015AFL Rising Star nominee: 2011