Former champions Eintracht Braunschweig returned to the Bundesliga after a 28-year absence when a 1-0 win at Inglostadt 04 on Friday secured a top-two finish in the second tier with three games left.
Braunschweig, Bundesliga champions in 1967 and relegated in 1985, join Hertha Berlin in winning automatic promotion.
"It is an amazing day," coach Torsten Lieberknecht told reporters as celebrations kicked off with a beer shower on the pitch. "The tears we shed will not be the last ones."
Braunschweig have 65 points, one fewer than Hertha. Third-placed Kaiserslautern, on 52, have four games to play.
Damir Vrancic scored the only goal with a last-gasp free-kick.