Early glories The club was founded in 1897 and obtained its first of 12 titles as Champion of Belgium in 1904. Their
matricule is 10. From 1933 to 1935 the team played 60 consecutive matches undefeated, setting a still unbeaten record in Belgium, winning three league titles in a row across that period led by captain
Jules Pappaert. With its first national title barely a few years after its foundation, Union quickly became a superpower and supplier to the Belgian team for the Olympic Games in 1920. The 1935 success was the club's eleventh, a Belgian record that would not be broken until the emergence of
Anderlecht in the 1960s. Seven of those titles came before the outbreak of
World War One in 1914. Between 1958 and 1965, the club had a brief spell of European success, playing in the
Inter-Cities Fairs Cup and reaching the semi-finals in the
1958–60 edition after a two-legged victory against
A.S. Roma. In 1963, however, the club was relegated to the second division, and in 1980 even fell as low as the Belgian Promotion division, the fourth tier.
Lower division survival In the sixties, Union began to struggle, bouncing between the First and Second Division several times. In 1973, the club dropped out of the First Division and would not return for 48 years. Two years later in 1975, would come another relegation to the Third Division for the first time. Union bounced back to the Second Division after just one season, but an even bigger decline followed at the end of the 1970s, back-to-back relegations seeing Union fall from the Second Division to the Fourth in successive years. The club rallied in the mid-80s to earn back-to-back promotions back up to the Second Division, claiming the Fourth Division crown in 1983 and the Third the following season. But no further progress could be made and Union would move between the second and third flights for close on the next four decades. Promotion back to the Second Division in 2004 saw two subsequent seasons of Union battling against relegation, but the 2006–07 season started brightly for Union. Promotion back to the First Division was a prospect, until a poor climax to their campaign post-Christmas, leading to the sacking of coach Tshupula Kande, replaced by Alex Czerniatynski. In May 2007, long-standing clubchairman Enrico Bove resigned along with several other members of the board of directors, and the club suffered another relegation to the Third Division. Bove returned as chairman in 2010 with the backing of new Italian sponsors, but Union's prospects on the pitch continued to suffer. In 2012–13, Union SG finished 17th out of 19 clubs in the Third Division B, inside the relegation zone. However, KVK Tienen were found guilty of making irregular payments and were automatically relegated to the Fourth Division, earning Union a reprieve via a play-off, which they won 1–0 against RFC de Liège. Union went on to finish a creditable third in the
2014–15 Belgian Third Division, but again would prosper from other clubs’ problems, as the top two of Cappellen and Sprimont Comblain Sport both passed up applying for a Second Division licence, so Union were promoted in their place.
Revival and return to the First Division On 21 May 2018,
Tony Bloom, chairman of
English Premier League side,
Brighton & Hove Albion was confirmed as the majority shareholder. Current Union chairman Alex Muzio was a co-investor with Tony Bloom in 2018. On 7 July 2023 Alex Muzio was confirmed as having become the majority owner of Union.
Title contenders and European football 2021–22: Top of regular season, Play-offs runner-ups A sensational return to top-flight football after 48 years away saw a 3–1 opening-day win away to Brussels' traditional giants Anderlecht. Union in their next match a week later hosted reigning champions
Club Brugge on 1 August 2021 in their first home game in the top division since 1973, being edged out 1–0 through a late
Eduard Sobol winner. Union went top of the Pro League on 17 October 2021, passing previous leaders
Eupen by virtue of a 4–1 win over
Seraing, and would remain there until May. Due to the novelty of being crowned unofficial
winter champions, Union were awarded a special trophy by the newspaper HLN. In a difficult January run against all of the previous season's top four, Union beat Anderlecht,
Genk and
Royal Antwerp, drawing 0–0 away to Club Brugge. By the end of the regular season, Union were top on 77 points, five ahead of Club Brugge, with Antwerp and Anderlecht also qualifying for the six rounds of play-offs, where the quartet would bring forward half of the regular season points into the play-offs. Hence, Union would resume on 39, Club 36, with Anderlecht and Antwerp both on 32. with Club going top under the "half-points" rule, as Union had needed their tally from the regular season rounded-up. Club Brugge won the midweek return 1–0 at the Jan Breydel through a rebounded own goal from goalkeeper
Anthony Moris to take a three-point lead with two games to go. A late equaliser from
Casper Nielsen was disallowed by
VAR for offside. Club Brugge clinched the league crown in their next (and penultimate) game against Royal Antwerp, despite Union beating Anderlecht for the fourth time in the season 2–0 at
Lotto Park. Eventually, Union finished four points down on Club in second place, with 46 points compared to Club's 50, historically qualifying Union for the
UEFA Champions League. League glory for Union would have seen them become the first newly promoted side to win a top-20 European national league championship at the first attempt since
Kaiserslautern's 1998 Bundesliga success. During their run for the title, coach
Felice Mazzu gained a reputation for dancing in front of Union's fans post-match, cited as keeping a light atmosphere within the club and maintaining a close relationship with the Union fans. Union's runners-up spot qualified them for the UEFA Champions League qualifiers, sending them into European football for the first time since 1964–65, and their first UEFA competition after featuring in five editions of the Fairs Cup in the 1950s and 60s. After going into first place in October, Union were top for 200 consecutive days.
2022–23: European participation and title contestant Despite an early exit from the
UEFA Champions League at the hands of
Rangers after a 2–0 "home" win at
OH Leuven's
Den Dreef stadium and a 3–0 loss at
Ibrox, Union dropped into the
UEFA Europa League and won their group, earning four victories from their six games against
Union Berlin,
Braga and
Malmö. A last-16 reunion with Union Berlin saw the Brussels club draw 3–3 away in Berlin, and win their "home" return 3–0 at Anderlecht's
Lotto Park. The quarter-finals had them paired with another
Bundesliga side in
Bayer Leverkusen, who defeated them 5–2 on aggregate (1–1 away, 1–4 home). Domestically, Union continued their remarkable form from the season before, lying second heading into the final round of the
Belgian Pro League regular season and reaching the
Belgian Cup semi-finals, only to lose to Royal Antwerp on penalties. Union reached the final day of the title play-offs in second place on 46 points, with leaders Antwerp also on 46, top by virtue of finishing in first place at the end of the regular season. Third-placers Genk were a point behind on 45. Union would be champions if they won their game against Club Brugge, and Antwerp did not win theirs against Genk. No other scenario would crown Union as champions. On the final matchday of the Play-offs, Union were leading 1–0 at home against Club Brugge in the 89th minute, and with Racing Genk leading Royal Antwerp 2–1 at the
Cegeka Arena, Union were on the way to being champions, with the Pro League trophy being flown via helicopter to the Joseph Marien Stadium. However, three late goals from Club Brugge - two in stoppage-time - and a late Antwerp equaliser from
Toby Alderweireld sent the crown Antwerp's way. Union's second consecutive title-race collapse saw them drop to third place which qualified them to the
Europa League play-off round.
2023–24: European adventure and title contention Owing to a third-place finish in the last season, Union entered in the
playoff round of the Europa League. There, they faced
FC Lugano and won, qualifying for the
Europa League group stage for the second consecutive season. In the group, they were drawn with
Liverpool,
Toulouse and
LASK. They would finish third in the group, but they secured some great results like their 2–1 win over Liverpool. In the
UEFA Europa Conference League knockout round playoffs, they were drawn against
Eintracht Frankfurt. The first leg finished 2–2, but they won the second leg in Frankfurt 2–1 to win 4–3 on aggregate and qualify for the round of 16 where they lost to
Fenerbahce. Following their 2–0 away win over
OH Leuven on 2 March 2024, Union mathematically became the regular season champions for the second time in three seasons, as they had an 8-point lead over city rivals
Anderlecht with only two regular season matchdays to go. On 9 May 2024, Union won their first Cup title after 110 years, following a 1–0 win over
Royal Antwerp in the
final. In the Champions' Play-offs, Union suffered four consecutive defeats which saw them drop to third place behind rivals Anderlecht and Club Brugge, followed by two wins against Antwerp and two draws against the other two title contenders which minimized their chances to secure the title for the third attempt in a row. Following victories over Cercle Brugge and Genk, Union finished as runners-up, just one point behind the champions, Club Brugge.
2024–25: Historic title triumph . Union started the
2024–25 season under new coach
Sébastien Pocognoli with a 2–1 away win over Club Brugge in the
Belgian Super Cup, securing their first ever title in the competition. They entered in the third qualifying round of the league phase of the
Champions League, but lost 4–1 to
Slavia Prague on aggregate. This loss did however grant them automatic entry into the
Europa League league phase, where they would finish 21st and advance to the knockout playoffs round as an unseeded team. They were drawn against
Dutch side
AFC Ajax in the playoffs round. Domestically, they enjoyed a historic league campaign. After finishing the regular season in third place behind Genk and Club Brugge, they entered the
Championship Playoffs in strong form. They went unbeaten in the playoffs, winning nine matches and drawing once. Their impressive run included a crucial 1–0 away win over playoff leaders Club Brugge. On the final matchday, a 3–1 victory over
Gent sealed their first top-flight title in 90 years, finally achieving glory after three previous near-misses since their promotion. The triumph also secured their first-ever spot in the
Champions League league phase for the following season. == Club culture and supporters ==