SPAL were promoted to Serie A on Saturday despite suffering a 2-1 defeat away to relegation-threatened Ternana.
The three-way battle for the two automatic promotion places looked set to be going down to Thursday's final day, but Fabio Ceravolo's injury-time winner for Benevento against third-placed Frosinone sealed promotion for SPAL.
SPAL, which stands for Societa Polisportiva Ars et Labor, have spent 21 seasons in the top flight in Italy, but the last of those came in 1967-68. The club suffered bankruptcy in 2005 and 2012 but reformed both times and will now return to Serie A.
Their best-ever finish in Serie A was fifth in 1959-60.
Coach Leonardo Semplici told Gazzetta dello Sport that his team's togetherness was the key.
"We have done an extraordinary job. Thank you to the club and to our fans," Semplici said. "We have all worked together and created the environment to do well.
"Nobody thought we could get to this point -- many said we would go down. It is very satisfying on a personal level too. I started from the bottom and I am happy.
"We have had an exceptional journey and done very well. I have trained men before anything else, then players."
Second place is between Hellas Verona and Frosinone, who must bridge a two-point gap. Verona wasted a chance to secure promotion on Saturday, drawing with Carpi 1-1.
The top two finishers are promoted directly while third-place can be promoted directly if they holds a 10-point lead over fourth -- otherwise there are playoffs. Frosinone are eight points ahead of fourth-placed Citadella entering the final round.