| Club: | Royale Union Saint-Gilloise |
| Season: | 2023–24 |
| Chairman: | Alex Muzio |
| Manager: | Alexander Blessin |
| Stadium: | Joseph Marien Stadium |
| League: | Belgian Pro League |
| League Result: | 2nd |
| Cup1: | Belgian Cup |
| Cup1 Result: | Winners |
| Cup2: | UEFA Europa League |
| Cup2 Result: | Group stage |
| Cup3: | UEFA Europa Conference League |
| Cup3 Result: | Round of 16 |
| League Topscorer: | Mohamed Amoura (18) |
| Season Topscorer: | Mohamed Amoura (25) |
| Pattern La1: | _unionsg2324h |
| Pattern B1: | _unionsg2324h |
| Pattern Ra1: | _unionsg2324h |
| Leftarm1: | FFFFFF |
| Body1: | FFFFFF |
| Rightarm1: | FFFFFF |
| Shorts1: | 000055 |
| Socks1: | FFF200 |
| Pattern B2: | _unionsg2324a |
| Leftarm2: | FFFFFF |
| Body2: | FFFFFF |
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| Prevseason: | 2022–23 |
| Nextseason: | 2024–25 |
The 2023–24 season was Royale Union Saint-Gilloise's 126th season in existence and third consecutive in the Belgian Pro League. They also competed in the Belgian Cup, UEFA Europa League and the Europa Conference League. They reached the final of and won the Belgian Cup for the first time since 1914.
| Player | Transferred from | Fee | Date | Source | ||
|---|---|---|---|---|---|---|
| Brann | €1,200,000 | [1] | ||||
| Jong PSV | Free | [2] | ||||
| Willem II | Free | [3] | ||||
| Kashima Antlers | €1,000,000 | [4] | ||||
| Argentinos Juniors | €1,500,000 | [5] | ||||
| Anderlecht | €1,400,000 | [6] | ||||
| Lugano | €4,000,000 | [7] | ||||
| Unattached | Undisclosed | [8] | ||||
| Independiente del Valle | Undisclosed | [9] | ||||
| Gent | €2,000,000 | [10] | ||||
| Sion | Loan | [11] |
| Player | Transferred to | Fee | Date | Source | ||
|---|---|---|---|---|---|---|
| SL16 FC | Undisclosed | [12] | ||||
| Reims | €3,600,000 | [13] | ||||
| Gent | €3,000,000 | [14] | ||||
 Mallorca | €2,500,000 | [15] | ||||
| Bologna | €2,000,000 | [16] | ||||
| Bayer Leverkusen | €20,000,000 | [17] | ||||
| Werder Bremen | €2,100,000 | [18] | ||||
| Feyenoord | €2,000,000 | [19] | ||||
| KV Kortrijk | Undisclosed | |||||
| Lierse | Loan | |||||
| Dender | Loan | [20] | ||||
| Plymouth Argyle | Released | [21] |
See main article: 2023–24 Belgian Pro League.
The league fixtures were unveiled on 22 June 2023.[22]
Union Saint-Gilloise finished first in the regular season and will start the Champions' play-offs on 35 points, their nearest rivals Anderlecht start three points behind them.
See main article: 2023–24 Belgian Cup.
See main article: 2023–24 UEFA Europa League.
The draw for the play-off round was held on 7 August 2023.
See main article: 2023–24 UEFA Europa League group stage.
The draw for the group stage was held on 1 September 2023.
See main article: 2023–24 UEFA Europa Conference League.
See main article: 2023–24 UEFA Europa Conference League knockout phase.
The draw for the knockout round play-offs was held 18 December 2023.
The draw for the round of 16 was held on 23 February 2024, Union Saint-Gilloise were unseeded in the draw and was prevented from drawing Club Brugge as clubs from the same association can not play in this round.
|-! colspan=14 style=background:#dcdcdc; text-align:center|Goalkeepers|-! colspan=14 style=background:#dcdcdc; text-align:center|Defenders|-! colspan=14 style=background:#dcdcdc; text-align:center|Midfielders|-! colspan=14 style=background:#dcdcdc; text-align:center|Forwards|-! colspan=14 style=background:#dcdcdc; text-align:center|Players who have made an appearance this season but have left the club|}