After squandering a two-goal lead in the final moments of their match on the Ligurian coast, the Venetians thought they would have to wait another week to book their ticket to Serie A.
That was until Mantova scored a 96th-minute winner to beat third-placed Monza 3-2 and ensure promotion for Venezia ahead of the final matchday.
With 79 points, the Lagunari are guaranteed to finish in one of the top two places in the league, which means automatic promotion to the top flight.
Venezia, owned by American investors since 2015, will begin their 15th season in the top flight in August and will aim to avoid the yo-yo effect of returning to Serie B after just one season, as has happened following their three previous promotions.
They could be joined automatically in Serie A by Frosinone, who moved into second place on 78 points on Friday at Monza's expense.
Having won 1-0 at Juve Stabia, Frosinone are three points clear of Monza and need just one point to secure their fourth season in Serie A.
The third ticket to the top flight will be decided in play-offs featuring the teams ranked third to eighth at the end of the regular season.