However, this great moment was not meant to be the culmination but the beginning of more successes. The Pride of Podlasie want to grow, building their own and Polish football's future.
Wednesday's Polish Cup quarter-final between Legia and Jagiellonia, which ended 3-1 to the Warsaw club was supposed to be a de facto final, but ended in a huge refereeing controversy.
With the whole of Poland discussing the mistakes, the Jaga coach Adrian Siemieniec closed the chapter and moved on.
The 33-year-old said: "I won't be provoked into judging the work of the referees, I never do that. Of course, the disappointment is big because we lost. But I know what to do, what to focus on, what direction to work in with the team."
Jaja are left with the Ekstraklasa (the Polish league) and the UEFA Conference League to focus on. This is how the Bialystok club works - it draws conclusions and moves forward.
The perfect deal
Before the championship success of 2023/24, a small revolution was carried out at Jagiellonia, and it was by no means limited to changes in the squad - above all it concerned the back offices.
In February 2022, Wojciech Pertkiewicz became the president and immediately hired sporting director Lukasz Maslowski, today the most sought-after man on the Polish market.
When coach Maciej Stolarczyk said goodbye in 2023, the two did not intend to do what most Polish clubs do - look for an experienced Ekstraklasa coach currently without a contract.
Instead, they opted for an assistant, the then 30-year-old Siemieniec. As it turned out, they knew what they were doing.
Young, funny and out of the box
Siemieniec was not a footballer, starting his coaching career at the age of 21. His work appealed to the nationally renowned Ireneusz Mamrot, who took him under his wing in 2014, and Siemieniec followed him through clubs such as Chrobry, Jagiellonia, Arka and LKS Lodz, until together they returned to Bialystok in 2021.
First, he led the reserves on his own, before replacing the sacked Stolarczyk in April 2023. The step surprised many, as Jaga were then in 14th place with a two-point gap to the relegation zone, and that spectre was hanging over them. Siemieniec kept the team in the Ekstraklasa and stayed on for another season, which turned out to be historic.
Under his leadership, Jagiellonia began to play very attacking football. It didn't matter how many goals their opponents scored, what mattered was that Jaga had one goal more at the end.
Siemieniec broke the pattern that you have to be a good footballer to become a coach at the highest level. Jagiellonia became a revelation in the league, but few said they would be able to win the Polish championship - Siemieniec did just that.
In his first full season as a coach in the Ekstraklasa, he rubbed the noses of many respected veterans and crowned the entire campaign with a historic title for Jagiellonia, who had never been champions before.
They won the championship in the last round, ending the season with 63 points - the same as runner-up Slask Wroclaw - but with a crazy goal difference.
Siemieniec's team scored 77 goals in 34 rounds (second only to Pogon Szczecin's 59) and conceded as many as 45 (even Warta Poznan, who were relegated from the league, had fewer).
Siemieniec himself, before joining the championship fete after the last game of the season, went to Warta's dressing room to console his rivals after the defeat.
A wide and solid squad without the millions
Jagiellonia as a club are trendsetters in Polish football. The Bialystok players do not have a multi-million pound budget to throw money around.
While the richest club Legia had a revenue of almost 270 million zlotys (65 million euros), Jaga was average with 60 million (14.5 million euros) and still won the league. There, every zloty counts, hence, moves to the club are very deliberate, almost always without a transfer sum.
Jaga had the foundation, which is based on the legend of the whole team, Jesus Imaz. The Spaniard arrived in Bialystok in the winter of 2019, when Wisla Krakow was having financial problems and Imaz was its star player.
Today, he has played 206 games in the colours of the current Polish champion, scoring 90 goals and recording 31 assists.
But Imaz's arrival is a thing of the distant past. Jagiellonia now specialises in bringing in quality 'free players' and loaning in solid footballers to strengthen the squad, which was not a regular practice in Poland. Clubs didn't like to "stall" footballers for others, but Jaga is changing that. They know what quality footballers from bigger clubs can give their squad.
This season, the likes of Darko Churlinov from Burnley, Peter Kovacik from Como, who was sent back, and Joao Moutinho from Spezia were sent on loan to the Polish champions for the whole season.
In the winter, Jaga also loaned Edi Semedo from Aris Limassol and Enzo Ebosse from Udinese for six months, while Leon Flach, who was valued at €3 million and played for Philadelphia Union in MLS, also arrived in Bialystok as a 'free agent' in the same window.
The big signing for Jagiellonia, though, was Afimico Pululu. He arrived in Bialystok as a free agent in the summer of 2023.
He had previously played for FC Basel and Greuther Furth, and there he did not have a great career, but at Jagiellonia, they saw potential in him at virtually no cost. It has worked out well.
Pululu has now played 70 games for the Polish champions, scoring 30 goals and recording nine assists in them, according to Opta, showing off a shooting accuracy of 62.1% and an xG of 5.55. He is particularly great in the Conference League, where he is the leader of the scoring classification with six goals.
It was an excellent move for the Podlasie Pride, who now have a great footballer and can also earn good money on him with a possible transfer. The Angolan is a 25-year-old, so there is sales potential in him. And he can bring several million zlotys into the coffers, as was the case with Bartlomiej Wdowik (transfer to Sporting Braga) or Dominik Marczuk (transfer to Real Salt Lake).
After the surprising championship, few believed that Jagiellonia would be able to afford to fight for solid results, as playing on three fronts (league, cup, Europe) was usually an excuse for inferior results in Poland.
Experts said that they did not have enough quality and that there was not enough rest for the players.
This line of thinking was broken by Siemieniec, smiling from ear to ear. Jagiellonia, under his leadership, advanced to the play-off stage of the Conference League, where they will face Cercle Brugge in the round of 16.
They are third in the Ekstraklasa table, two points behind leaders Lech Poznan, and elimination from the Polish Cup came after a match between the two main favourites.
For Siemieniec, there is no excuse for having to play every few days. His team goes out on the turf and gives their all.
He is only 33 years old, so he is at the beginning of his coaching career, and he can already be an example not only for the new generation of coaches but it can also open the minds of the old school.
Someone might say that professional cooperation between the director, president and manager is a normal procedure, but not in the Polish football pyramid. Jaga has shown that such a scheme allows success to be achieved very quickly, which is why fans all over the country dream of it becoming a standard in their clubs as well.