Ugo Humbert defeated Andrey Rublev in the final 6–3, 7–6^(7–4), to win the singles tennis title at the 2021 Halle Open. Humbert's win earned him his third career ATP Tour singles title and his first ATP 500 victory, and also made him the first French player to win the tournament since Henri Leconte won the inaugural edition in 1993.^[1][2] Both Humbert and Rublev were contesting their first career final on grass.^[3]

Roger Federer was the defending champion from when the event was last held in 2019,^[4] but he lost in the second round to Félix Auger-Aliassime.^[5]

	Semifinals							Final
		Félix Auger-Aliassime	4	6	65
		Ugo Humbert	6	3	77
									Ugo Humbert	6	77
								4	Andrey Rublev	3	64
	4	Andrey Rublev	6	3	6
	Q	Nikoloz Basilashvili	1	6	3

	First round							Second round							Quarterfinals							Semifinals
	1	D Medvedev	66	3
		J-L Struff	78	6					J-L Struff	77	3	4
		V Pospisil	64	66				Q	M Giron	61	6	6
	Q	M Giron	77	78											Q	M Giron	3	2
		F Auger-Aliassime	6	7												F Auger-Aliassime	6	6
		H Hurkacz	3	5					F Auger-Aliassime	4	6	6
	Q	I Ivashka	64	5				5	R Federer	6	3	2
	5	R Federer	77	7																			F Auger-Aliassime	4	6	65
	3	A Zverev	6	3	6																		U Humbert	6	3	77
		D Koepfer	4	6	3			3	A Zverev	64	6	3
		U Humbert	4	77	77				U Humbert	77	3	6
		S Querrey	6	64	65											U Humbert	6	65	6
	Q	R Berankis	3	6	2											S Korda	2	77	4
		K Nishikori	6	2	6				K Nishikori	6	3	5
		S Korda	6	77					S Korda	2	6	7
	6	R Bautista Agut	3	60

	First round							Second round							Quarterfinals							Semifinals
	7	D Goffin	6	5	0r
		C Moutet	1	7	0				C Moutet	4	64
	SE	J Rodionov	4	3				WC	P Kohlschreiber	6	77
	WC	P Kohlschreiber	6	6											WC	P Kohlschreiber	64	2
		J Thompson	6	77											4	A Rublev	77	6
	WC	D Altmaier	2	64					J Thompson	4	4
		K Khachanov	3	65				4	A Rublev	6	6
	4	A Rublev	6	77																		4	A Rublev	6	3	6
	8/WC	G Monfils	4	4																		Q	N Basilashvili	1	6	3
		L Harris	6	6					L Harris	6	710
		G Pella	77	5	1			Q	L Lacko	3	68
	Q	L Lacko	65	7	6											L Harris	4	65
	Q	N Basilashvili	6	3	6										Q	N Basilashvili	6	77
		G Simon	1	6	4			Q	N Basilashvili	6	7
	Q	A Rinderknech	7	6				Q	A Rinderknech	2	5
	LL	Y Hanfmann	5	3

1. Yannick Hanfmann

	First round							Qualifying competition
	1	Nikoloz Basilashvili	79	77
	WC	Rudolf Molleker	67	65
								1	Nikoloz Basilashvili	77	6
								7	Yannick Hanfmann	63	4
		Alexandre Müller	6	0	5
	7	Yannick Hanfmann	2	6	7

	First round							Qualifying competition
	2	Egor Gerasimov	4	5
	PR	Lukáš Lacko	6	7
								PR	Lukáš Lacko	4	6	6
								11	João Sousa	6	4	3
		Grégoire Barrère	6	65	4
	11	João Sousa	3	77	6

	First round							Qualifying competition
	3	Marcos Giron	6	7
	WC	Dominic Stricker	4	5
								3	Marcos Giron	6	77
								9	Daniel Elahi Galán	4	65
	WC	Nicola Kuhn	62	6	64
	9	Daniel Elahi Galán	77	4	77

	First round							Qualifying competition
	4	Radu Albot	6	3	5
		Christopher O'Connell	4	6	7
									Christopher O'Connell	6	4	2
								12	Arthur Rinderknech	3	6	6
		Sergiy Stakhovsky	4	4
	12	Arthur Rinderknech	6	6

	First round							Qualifying competition
	5	Ilya Ivashka	6	6
	PR	Tatsuma Ito	1	3
								5	Ilya Ivashka	2	6	6
								8	James Duckworth	6	4	0
		Ernests Gulbis	7	5	2
	8	James Duckworth	5	7	6

	First round							Qualifying competition
	6/Alt	Ričardas Berankis	6	2
		Cedrik-Marcel Stebe	4	1r
								6/Alt	Ričardas Berankis	6	6
								10	Dennis Novak	4	3
		Yannick Maden	4	0r
	10	Dennis Novak	6	0

• Main draw
• Qualifying draw