The BVB secured a UEFA Champions League berth for next season after first-half goals from Raphael Guerreiro and Marco Reus paved the way for a 3-1 win over Mainz in the closer of the 33rd round in Bundesliga on Sunday.
Dortmund started highly motivated into the encounter and dominated possession while Mainz defended deep and lurked for counterattacking opportunities.
The visitors staged a powerful opening period but had to wait until the 23rd minute before Jadon Sancho's lay-up allowed Guerreiro to open the scoring with a well-placed shot into the top-right corner.
Mainz was unable to keep Dortmund at arm's length as Reus tested Finn Dahmen with a dangerous long-range effort before the German international eventually made it two before the break after tapping home Sancho's second assist in the 42nd minute.
After the restart, Mainz took over and had several chances but neither Karim Onisiwo nor substitute Robin Quaison was able to reward the hosts for their lively opening period.
Dortmund reacted well and responded with attacks, but Jude Bellingham and Sancho pulled wide at the other end of the pitch as both sides traded attacks.
Edin Terzic's men however sealed the deal in the 80th minute when Erling Haaland sent Julian Brandt through, who finished the job into the open goal after rounding the onrushing Dahmen.
The hosts scored a consolation goal in the dying seconds of the game after Thorgan Hazard conceded a handball penalty, allowing Quaison to slot home from the spot to make it 3-1.
With the result, the BVB climbs to third while Mainz slips to the 13th position in the standings.
Elsewhere, runner-up Leipzig bounced back from two goals down and sewed up a 2-2 draw with Wolfsburg to seal a second-place finish. The Wolves slip from the third to the fourth spot, but they will nevertheless play in Europe's elite competition next season.
"I think above all the most important fact is that we wrapped up a ticket for Champions League next season. Before the season, no one thought we would be able to snatch a top-four finish," Wolfsburg head coach Oliver Glasner said.