| Date: | 8–13 June |
| Edition: | 43rd |
| Category: | ATP Tour 250 |
| Draw: | 28S / 16D |
| Prize Money: | €543,210 |
| Surface: | Grass |
| Location: | Stuttgart, Germany |
| Venue: | Tennis Club Weissenhof |
| Champs: | Marin Čilić[1] |
| Champd: |  Marcelo Demoliner /  Santiago González[2] |
| Main Name: | Stuttgart Open |
| Before Year: | 2019 |
The 2021 MercedesCup was a men's tennis tournament played on outdoor grass courts. It was the 43rd edition of the Stuttgart Open, and part of the ATP Tour 250 series of the 2021 ATP Tour. It was held at the Tennis Club Weissenhof in Stuttgart, Germany, from 8 June until 13 June 2021. Unseeded Marin Čilić won the singles title.
See main article: 2021 MercedesCup – Singles.
Félix Auger-Aliassime, 7–6(7–2), 6–3See main article: 2021 MercedesCup – Doubles.
Marcelo Demoliner / Santiago González defeated Ariel Behar / 
Gonzalo Escobar, 4–6, 6–3, [10–8]| Event | W | F | SF | QF | Round of 16 | Round of 32 | width=85 | Q | width=85 | Q2 | width=85 | Q1 |
| Singles | 250 | 150 | 90 | 45 | 20 | 0 | 12 | 6 | 0 | |||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Doubles | 0 |
| Event | W | F | SF | QF | Round of 16 | Round of 32 | width=85 | Q2 | width=85 | Q1 |
| Singles | €53,280 | €38,200 | €27,195 | €18,130 | €11,660 | €7,010 | €3,425 | €1,780 | ||
| Doubles* | €19,880 | €14,240 | €9,390 | €6,090 | €3,580 |
| Country | Player | Rank1 | Seed | |
|---|---|---|---|---|
| Canada | Denis Shapovalov | 14 | 1 | |
 Poland | Hubert Hurkacz | 17 | 2 | |
| Canada | Félix Auger-Aliassime | 21 | 3 | |
 Australia | Alex de Minaur | 22 | 4 | |
 Georgia | Nikoloz Basilashvili | 30 | 5 | |
 France | Ugo Humbert | 31 | 6 | |
| France | Adrian Mannarino | 36 | 7 | |
| Australia |
The following players received wildcards into the main draw:
The following players received entry from the qualifying draw:
The following player received entry as a lucky loser:
Alexander Bublik → replaced by Alexei Popyrin
Taylor Fritz → replaced by Marin Čilić Jordan Thompson
Aslan Karatsev → replaced by Jérémy Chardy Reilly Opelka → replaced by Lloyd Harris Benoît Paire → replaced by Sam Querrey Milos Raonic → replaced by 
Márton Fucsovics
Jannik Sinner → replaced by Dominik Koepfer Lorenzo Sonego → replaced by 
Guido Pella
Feliciano López
Ilya Ivashka Gilles Simon| Country | Player | Country | Player | Rank1 | Seed | |
|---|---|---|---|---|---|---|
 United Kingdom | Jamie Murray | Brazil | Bruno Soares | 33 | 1 | |
| France | Jérémy Chardy | France | Fabrice Martin | 58 | 2 | |
| Raven Klaasen |  Japan | Ben McLachlan | 67 | 3 | ||
 New Zealand | Marcus Daniell |  Austria | Philipp Oswald | 75 | 4 |
The following pairs received wildcards into the doubles main draw:
The following pairs received entry as alternates:
Félix Auger-Aliassime / Nicholas Monroe Nikoloz Basilashvili / 
Divij Sharan Gonzalo Escobar Marcelo Demoliner / Santiago González Máximo González / Andrés Molteni Hubert Hurkacz / Łukasz Kubot Oliver Marach / 
Aisam-ul-Haq Qureshi
Frederik Nielsen / Jean-Julien Rojer Luke Saville / Jordan Thompson Rohan Bopanna / Franko Škugor → replaced by Oliver Marach / Aisam-ul-Haq Qureshi Alexander Bublik / Reilly Opelka → replaced by Ariel Behar / Gonzalo Escobar
Sander Gillé / Joran Vliegen → replaced by Máximo González / Andrés Molteni Frederik Nielsen / Jean-Julien Rojer Sebastian Korda / Rajeev Ram → replaced by Marcelo Demoliner / Santiago González John Peers → replaced by Félix Auger-Aliassime / Nicholas Monroe Łukasz Kubot / Marcelo Melo → replaced by Hubert Hurkacz / Łukasz Kubot Adrian Mannarino / Benoît Paire → replaced by Nikoloz Basilashvili / Divij Sharan Michael Venus → replaced by Luke Saville / Jordan Thompson
