Bratt was selected by the Devils in the sixth round (No. 162) of the 2016 NHL Draft after he scored four points (two goals, two assists) in seven games for Sweden at that year's Under-18 5-Nations Tournament.
After signing a three-year, entry-level contract with the Devils on May 13, 2017, he became the lowest drafted teenager to play in the NHL since 1995-96, when center Roman Vopat (No. 172, 1994) and forward Richard Zednik (No. 249, 1994) played for the St. Louis Blues and Washington Capitals, respectively.