The club was established on the 24th of October, 1920. it's name, Osasuna, was chosen by Benjamin Andoian Martinez. 14) When Spanish football turned official in 1928 Osasuna got a place in the 3rd division. They gained an upgrade to Segunda Division after the 1931-32 season when they won the playoff match against Nacional de Madrid. They were promoted into La Liga three seasons later. The same year they made it to the semi-finals of Copa del Rey and lost to Sevilla. The following season, Osasuna made it to the semi-finals once more and lost this time to Barcelona over two legs even though they won one of the legs.
The club was severely harmed by the brutal rearguard repression imposed in the hands of Nationalist rebels during the 1936 coup-de-etat that overthrew the Spanish Second Republic. A minimum of ten employees, players and board members were killed and imprisoned, or else repressed. The survivors were forcibly recruited to fight in an army, with a few of them expressing passion for the putsch. The strong support from Navarre to the Nationalist rebels resulted in Osasuna receiving a spot into the 1940s La Liga when official competitions were resumed, even though they finished last in 1935-36 , and ought to have been dropped but a play-off was set up with the other demolished side Atletico Aviacion - associated with the Spanish Air Force and thus favorably favored to the ruling military. The Madrid team prevailed and, with the help of their strong supporters and supporters, won the title of league champion and keep the title. It was not until 1953-54 that Osasuna played in the top division. It was 1956-57, when they were able to maintain their spot among the elite, staying there for three more years.
In the month of September, 1967 the Osasuna's El Sadar Stadium was opened with a game with Osasuna with Vitoria de Setubal. The match ended with Osasuna winning 3-0 for the hosts. The club was awarded its first UEFA Cup qualification in 1985-86 after finishing sixth in the league. their tournament began in the opening round, sweeping aside Scottish club Rangers and then being eliminated in the second round by Belgian club Waregem with a score of 3-2 in an aggregate. In the 1990-91 campaign, Osasuna placed third in their league and which was their most successful league finish to the time of. This earned them a place in the next year's UEFA Cup, where the club advanced to the third round, defeating Slavia Sofia, as well as Stuttgart. In 1993-94, they finished last. the club remained in the second division, until finally getting promoted in 1999-2000 , after finishing at the top of league tables.
The 2002-03 Copa del Rey, Osasuna reached the semi-finals its first time since the 1988 season. The team was in the competition during the first round in which they beat Lemona. In the next round they defeated Eibar, Real Union and Sevilla up to the semi-finals in which they were eliminated following defeating Recreativo de Huelva, 4-2 in the aggregate.
The team in 2005 made it to in the Copa del Rey final for the first time, but lost in the final to Real Betis after extra time. They suffered a difficult time during the Copa Del Rey, almost losing at the end of the 64th round before just barely defeating Segunda Division B side Castellon with penalties following an uncontested draw. They then beat Girona by 1-0 after extra-time, before beating Getafe, Sevilla and Atletico Madrid each by a single goal to reach the final.
On the 27th of November, 2005 Osasuna was playing their thousandth league game La Liga. After a fantastic domestic campaign in 2005-06 the club made history when they finishing fourth with the top finish of all time and advancing to the qualifying stage for the UEFA Champions League in the next season. This feat was made even more impressive by the tension that kept up until the final day of the tournament, in which Osasuna as well as Sevilla were both fighting for fourth place. Both had the same amount of points, however Osasuna was able to finish higher thanks to their head-to-head results. However, they failed to reach the Champions League group phase, after being eliminated by Hamburger SV in the third qualifying round. This left Navarrese to play in the UEFA Cup for the fifth time.
Osasuna were selected in the Group D of the 2006-07 UEFA Cup, and qualified for knockout phase having finished second within the group. They were in the round of 32 they received a draw against Bordeaux which won with a 1-0 aggregate. They also drew at home 0-0 and then winning by 1-0 in Pamplona with an extra-time victory scored from Javad Nekounam. The next opponent for Osasuna was Rangers which was a second time that Osasuna was successful following a 1-1 draw at Glasgow as well as a 1-1 victory at home. The club played German team Bayer Leverkusen in the quarter-finals. The team was regarded as an underdog. Osasuna didn't just advance into the semi-finals, but they did it in fashion (a 3-1 win away almost sealed the tie and the Rojillos also took the lead in the second leg 1-0). In the semi-finals of the tournament, the club were drawn with holders as well as the other Spanish team Sevilla and eventually lost 2 - 1 on aggregate following the team won 1-0 at home.
The following two seasons that followed, Osasuna suffered a lot throughout the season. In 2007-08 they finished 17th and just one point ahead of the possibility of relegation. In 2008-09, they managed to avoid relegation on the last day, finishing 18th and advancing to the final day of the match against Real Madrid, the club was a bit behind, but they came back by scoring two times (the decisive one was scored by Juanfran the Merengue student) to beat 9-man Los Blancos and remain in the top league with a 15th place finish.
Osasuna enjoyed great successes in 2011-12 in the 2011-12 season, finishing seventh and one position further from qualifying for European spots, but they suffered a similar setback in the following two seasons which saw them finish 16th in 2012-13 before being sent in the division 2 following finishing 18th in 2013-14. The 2014-15 season was the best, and the club was able to finish with a position one place above zone of relegation. The change in management led to significant improvement. Osasuna was victorious in the final match of the regular season 2015-16 losing 0-5 to Oviedo and finished at the sixth spot in the table, being promoted to the playoffs for promotion and. They then won all their playoff matches - including Gimnastic de Tarragona in the semi-finals and Girona at the end of their final in order to make it in La Liga once again. Osasuna finished 2016-17 in 19th position, resulting in relegation. They only managed 8th place in their first season returning to the second tier.
20 May, 2019 Osasuna was promoted back to La Liga after Granada's victory over Albacete which mathematically ensured the promotion spot with just three games remaining during the regular season. On the 31st of May they beat Cordoba to become the 2018-19 Segunda Division champions.
The club commemorated its centennial in the month of October 2020 by winning an 1-0 league win over Athletic Bilbao, albeit the game was played in a stadium with no seats due to restrictions brought on by the COVID-19 epidemic in Spain. In May 2021 after years of silence, and in conjunction with many other Navarrese institutions, the club's President Luis Sabalza paid homage for the first time to players who suffered through the rearguard Nationalist oppression in the Spanish Civil War, on behalf of the board of directors.
