| MagicJack | Women's Professional Soccer | Boca Raton | 2001 | — |
| Maine Sting | National Premier Soccer League | — | 2008 | — |
| Maine USL W League team | USL W League | Portland | — | — |
| Manhattan Celtic FC | Eastern Premier Soccer League | New York City | — | — |
| Manhattan SC | — | Riverdale | — | Gaelic Park |
| Maryland Bobcats FC | National Independent Soccer Association | New York City | 2010 | Maryland SoccerPlex |
| Maryland Mania | A-League | — | 1999 | — |
| Mass United FC | National Premier Soccer League | — | 2009 | — |
| Massachusetts Twisters | — | — | 2003 | The Big E Coliseum |
| Maunabo Leones | Liga Nacional de Fútbol de Puerto Rico | Maunabo | 1960 | — |
| Mayagüez FC | Puerto Rico Soccer League | — | 2004 | Mayagüez Athletics Stadium |
| Memphis 901 FC | USL Championship | Memphis | 8 January 2018 | AutoZone Park |
| Memphis Americans | Major Indoor Soccer League | — | 1981 | — |
| Memphis Express | USL League Two | — | 2002 | — |
| Memphis Rogues | North American Soccer League | Memphis | 1978 | — |
| Miami Americans | — | Miami | 1979 | — |
| Miami FC | USL Championship | Miami | 2015 | Pitbull Stadium |
| Miami Fusion | Major League Soccer | Fort Lauderdale | 1997 | Lockhart Stadium |
| Miami Fusion FC | National Premier Soccer League | — | 2014 | — |
| Miami Toros | North American Soccer League | Washington, D.C. | 1972 | Miami Orange Bowl |
| Michigan Stars FC | National Independent Soccer Association | Detroit | 1982 | Wisner Stadium |
| Milwaukee Rampage | A-League | Milwaukee | 1993 | Uihlein Soccer Park |
| Milwaukee Torrent | National Premier Soccer League | Milwaukee | January 2015 | — |
| Milwaukee Wave | Major Indoor Soccer League | — | 1984 | UW–Milwaukee Panther Arena |
| Minneapolis City SC | National Premier Soccer League | Minneapolis | 2015 | — |
| Minnesota Kicks | North American Soccer League | Minneapolis | 1976 | Metropolitan Stadium |
| Minnesota Kings | National Premier Soccer League | — | 2009 | — |
| Minnesota Strikers | North American Soccer League | Minneapolis | 1984 | Hubert H. Humphrey Metrodome |
| Minnesota Thunder | USL First Division, A-League | Blaine | 1990 | National Sports Center |
| Minnesota United FC | Major League Soccer | Minneapolis | 2015 | Allianz Field |
| Minnesota United FC | North American Soccer League | — | 2010 | National Sports Center |
| Mississippi Beach Kings | Eastern Indoor Soccer League | — | 1998 | Mississippi Coast Coliseum |
| Mississippi Brilla | USL League Two | Clinton | 2006 | — |
| Missouri Comets | Major Indoor Soccer League | — | 2010 | Independence Events Center |
| Montgomery United FC | USL League Two | Montgomery | 2024 | — |
| Montreal Manic | North American Soccer League | Montreal | 1981 | Olympic Stadium |
| Moreno Valley FC | United Premier Soccer League | — | 2015 | — |
| Morris County Colonials | National Premier Soccer League | — | 2007 | — |
| Motagua New Orleans | — | New Orleans | 1984 | Pan American Stadium |
| MP United F.C. | M*League Division 1 | Northern Mariana Islands | 2008 | — |
| Myrtle Beach FC | National Premier Soccer League | Myrtle Beach | 2011 | Doug Shaw Memorial Stadium |