In 2014, his junior year at Kenowa Hills High School, Brazier won the 800 meters at the New Balance national scholastic championships in 1:48.61; his time was a new Michigan state record.

[2][3] His times continued the drop in his senior year; he ran a 45.92 split on a 4 × 400 meters relay and improved his 800-meter best to 1:47.55, placing him fourth on the all-time national high school list.

[5] In summer 2015, Brazier attempted to earn an opportunity to represent United States on his first national team as a junior (U20) at 2015 Pan American Junior Athletics Championships to compete in the 800 m.[6] After graduating from high school after the 2015 season Brazier went to Texas A&M University, where he was coached by former top runner Alleyne Francique and head coach Pat Henry.

[13] Brazier turned professional after his NCAA victory, signing an endorsement deal with Nike and forgoing his three remaining years of collegiate eligibility.

[16] Donavan Brazier reconnected with his coach from Texas A&M University (Grenada’s top 400 m runner Alleyne Francique).

On August 29, 2019, Brazier set a new 800 meter personal best of 1:42.70 en route to winning the Diamond League meet in Zurich, Switzerland.