| Manicke x Kai Sri Lankan Restaurant & Cafe | Sri lankan restaurant | 7 Fenchurch Walk | Mon 11:00–14:30, 17:00–21:00 |
| MAPT | MaleAestheticsPT | Skin - Hair - Wellness | Skin care clinic | 78-81 Queens Rd | Mon–Thu 09:30–19:00 |
| Marlborough Productions | Theater production | The Old Courthouse, 118 Church St | Mon–Fri 10:00–18:00 |
| Martin Searle Solicitors | Employment lawyer | 9 Marlborough Pl | Mon–Fri 09:30–17:15 |
| Matlock Pharmacy | Travel clinic | 12 Matlock Rd | Thu 09:00–18:15 |
| Mayberry Garden Centre | Garden centre | 7-17 Old Shoreham Rd | Mon–Sat 08:30–18:00 |
| Mayfield Clinic Brighton | General practitioner | 18a Clermont Rd | Thu 09:00–18:00 |
| Mayo Wynne Baxter Solicitors Brighton | Property lawyer | Ground Floor, Napier House, Trafalgar Pl | Mon–Fri 08:30–17:30 |
| McKeown Psychology Associates Ltd. | Psychologist | 17 Prince Albert St | Mon–Fri 09:00–17:00 |
| McMillan Financial Advice | Financial planner | Floor 2, Spaces, 3 Fleet St | Mon–Fri 09:00–17:00 |
| MDTea | Tea wholesaler | Unit 27, Open Market, Marshalls Row | Mon–Sat 10:30–17:30 |
| Mercedes-Benz of Brighton | Mercedes-benz dealer | Victoria Rd | Mon–Fri 08:00–18:30 |
| Mermaid Brighton beauty salon | Beauty salon | 116 Dyke Rd | Mon–Thu 10:00–20:00 |
| Mexico Real Cafe | Tea and coffee shop | 4th Floor, 44 North Rd | Daily 08:00–18:00 |
| MGAC Brighton | Building consultant | 5th Floor, 98/99 Queens Road | Mon–Thu 08:30–17:30 |
| Michael Bloomstein Precious Metals | Gold dealer | 30 Gloucester Rd | Mon–Fri 09:00–17:00 |
| Milan Groundworks & Civil Engineers | Builder | 120 Old London Rd | Mon–Sat 08:00–18:00 |
| Mile Oak Farm | Farm | Mile Oak Rd | Mon–Sat 09:00–17:00 |
| Mishkin's Music Academy / Nest Studios | Piano instructor | 22 Kingsbury Rd | Daily 09:00–21:00 |
| MK Dental and Implant Clinic | Dentist | 17 Bristol Gardens | Thu 08:30–17:00 |
| Mobile Medi motor | Motorcycle shop | 7 Compton Ave | Mon–Wed 09:00–19:00 |
| Mobile Vehicle Repair Services | Mechanic | Car Key Hero, Smart Shop, 9 Station Rd | Mon–Sat 08:30–18:00 |
| Model Talent UK | Modelling agency | Royal Alexandra Quarter, 10 Beves, Dyke Rd | Daily 09:00–21:00 |
| Moksha Caffe | Brunch restaurant | 4-5 York Pl | Mon–Fri 08:00–16:00 |
| Money 4 Travel - Essiell Ltd | Software company | Park Gate, 161-163, Preston Rd | Daily 08:00–17:00 |
| Monster Studios | Rehearsal studio | Monster Studios, Maritime House, Basin Rd N | Daily 10:00–00:00 |
| MOONLIGHT Pan Asian Cuisine | Indonesian restaurant | 31-32 New Rd | Mon–Fri 12:00–22:00 |
| Motorway | Car auction | Motorway, 16, 17 West St | Daily 09:00–19:00 |
| Moulsecoomb Community Leisure Centre | Gym | Moulsecoomb Leisure Centre, Moulsecoomb Way | Mon 07:00–21:00 |
| Moulsecoomb Social Club | Social club | Moulsecoomb Hall, Lewes Rd | Mon–Tue 16:00–23:00 |