Defending champion Nikola Mektić and his partner, Mate Pavić, defeated Dan Evans and Neal Skupski in the final, 6–3, 4–6, [10–7], to win the doubles tennis title at the 2021 Monte-Carlo Masters. It was the all-Croatian duo's second consecutive ATP Tour Masters 1000 title together and their fifth title overall of the year. The win also earned Mektić his first successful career title defense. The match was the second successive encounter between both teams in consecutive Masters 1000 finals.^[1][2]

Mektić won the tournament when it was last held in 2019 with Franko Škugor,^[1] but Škugor did not return to compete.

Pavić and Robert Farah were in contention for the ATP No. 1 doubles ranking at the start of the tournament. After Farah lost in the semifinals, Pavić retained the top ranking by reaching the final.

	Semifinals							Final
	1	Juan Sebastián Cabal Robert Farah	60	6	[4]
		Dan Evans Neal Skupski	77	2	[10]
									Dan Evans Neal Skupski	3	6	[7]
								2	Nikola Mektić Mate Pavić	6	4	[10]
	4	Marcel Granollers Horacio Zeballos	6	5	[4]
	2	Nikola Mektić Mate Pavić	3	7	[10]

	First round							Second round							Quarterfinals							Semifinals
								1	JS Cabal R Farah	6	6
		F Auger-Aliassime H Hurkacz	5						F Auger-Aliassime H Hurkacz	0	2
	WC	R Arneodo H Nys	2r												1	JS Cabal R Farah	77	7
		F Fognini D Schwartzman	6	7												F Fognini D Schwartzman	65	5
		O Marach L Saville	4	5					F Fognini D Schwartzman	1	6	[10]
		A Mannarino B Paire	62	3				6	W Koolhof Ł Kubot	6	4	[7]
	6	W Koolhof Ł Kubot	77	6																		1	JS Cabal R Farah	60	6	[4]
																							D Evans N Skupski	77	2	[10]
								3	I Dodig F Polášek	6	65	[11]
		S Gillé J Vliegen	65	6	[8]				D Evans N Skupski	3	77	[13]
		D Evans N Skupski	77	3	[10]											D Evans N Skupski	1	77	[10]
		A de Minaur J Peers	63	6	[9]											R Klaasen B McLachlan	6	65	[4]
		R Klaasen B McLachlan	77	3	[11]				R Klaasen B McLachlan	61	6	[10]
		M Melo J-J Rojer	6	1	[8]			5	R Ram J Salisbury	77	3	[5]
	5	R Ram J Salisbury	4	6	[10]

	First round							Second round							Quarterfinals							Semifinals
	8	K Krawietz H Tecău	64	6	[9]
	WC	P Tsitsipas S Tsitsipas	77	3	[11]			WC	P Tsitsipas S Tsitsipas	4	4
		C Garín G Pella	4	77	[10]				C Garín G Pella	6	6
		J Murray J-L Struff	6	64	[5]											C Garín G Pella	3	1
		J Chardy F Martin	79	4	[4]										4	M Granollers H Zeballos	6	6
		K Khachanov A Rublev	67	6	[10]				K Khachanov A Rublev	3	1
								4	M Granollers H Zeballos	6	6
																						4	M Granollers H Zeballos	6	5	[4]
	7	P-H Herbert N Mahut	6	6																		2	N Mektić M Pavić	3	7	[10]
	WC	S Bolelli J Sinner	4	4				7	P-H Herbert N Mahut	77	7
		H Kontinen É Roger-Vasselin	6	6					H Kontinen É Roger-Vasselin	63	5
	Alt	A Bublik D Lajović	4	4											7	P-H Herbert N Mahut	3	1
	Alt	A Behar G Escobar	6	6											2	N Mektić M Pavić	6	6
		G Dimitrov D Goffin	4	3				Alt	A Behar G Escobar	4	6	[3]
								2	N Mektić M Pavić	6	1	[10]

• Main draw