| Champ: |  Casper Ruud |
| Runner: |  Pedro Martínez |
| Score: | 6–1, 4–6, 6–3 |
| Draw: | 28 |
| Seeds: | 8 |
| Type: | singles doubles |
See main article: article and 2021 Generali Open Kitzbühel.
Miomir Kecmanović was the defending champion, but chose to compete at the Summer Olympics instead.
Casper Ruud won his fifth ATP Tour title, defeating Pedro Martínez in the final, 6–1, 4–6, 6–3. It was Ruud's third consecutive title in as many weeks.
The top four seeds receive a bye into the second round.