Derrick Etienne Jr. scored the only goal against Orlando City at Red Bull Arena, giving his side a 1-0 victory.
The Red Bulls entered the day one point behind Atlanta United for the top spot, and they got some help to clinch the Shield.
Already eliminated from playoff contention after a miserable year, reigning champion Toronto FC downed Atlanta United 3-1, which allowed the Red Bulls to leapfrog the Five Stripes for the top spot in the league.
When all was said and done the Red Bulls had clinched their third Supporters Shield trophy, all of which have been won in the past six years (2013, 2015, 2018).
With a record of 22 wins, seven losses and five draws, the Red Bulls have sealed the largest points haul ever in an MLS season (71), breaking the record Toronto FC set last year (69).
The Red Bulls also set an MLS record for most wins in a season with their 22 victories.
Both New York and Atlanta had already clinched byes in the Eastern Conference playoffs, and the two teams will await the winners of the knockout round games in the Conference semifinals.