| Magnolia Basket Campobasso | — | Campobasso | 2017 | — |
| Maurolico Messina | — | — | — | — |
| Memphis Grizzlies | National Basketball Association | Memphis | 1995 | Pyramid Arena, FedExForum |
| Mens Sana Basket Siena | Lega Basket Serie A | Siena | 1861 | Palasport Mens Sana |
| Mercede Basket Alghero | — | Alguer | 1977 | — |
| Miami Dolphins | National Football League | Miami | 1966 | Hard Rock Stadium |
| Miami Heat | National Basketball Association | Miami | 1988 | Miami Arena, Kaseya Center |
| Miami Marlins | Grandes Ligas de Béisbol | — | 1993 | LoanDepot Park, Hard Rock Stadium |
| Milwaukee Braves | Grandes Ligas de Béisbol | Milwaukee | 1953 | Milwaukee County Stadium |
| Milwaukee Brewers | Grandes Ligas de Béisbol | Milwaukee | 1969 | American Family Field |
| Milwaukee Bucks | National Basketball Association | Milwaukee | 1968 | UW-Milwaukee Panther Arena, Bradley Center, Fiserv Forum |
| Minnesota North Stars | — | Bloomington | 1967 | Met Center |
| Minnesota Timberwolves | National Basketball Association | Minneapolis | 1989 | Hubert H. Humphrey Metrodome, Target Center |
| Minnesota Twins | Grandes Ligas de Béisbol | — | 1901 | Target Field, American League Park, Metropolitan Stadium, Hubert H. Humphrey Metrodome, Boundary Field, Griffith Stadium |
| Minnesota United Football Club | Major League Soccer | Minneapolis | 2015 | Allianz Field, Huntington Bank Stadium |
| Minnesota Wild | — | Saint Paul | 2000 | Grand Casino Arena |
| Miraflores Sporting Club | — | — | — | Antiguo Estadio Nacional del Perú |
| Modena Basket | — | — | — | — |
| Montecatini Terme Basketball | — | Montecatini Terme | 1949 | PalaTerme |
| Montigarda Basket | — | Montichiari | — | — |
| Montreal Expos | Grandes Ligas de Béisbol | — | 1969 | Estadio Olímpico de Montreal, Jarry Park Stadium |
| Montreal Maroons | — | — | 1924 | Forum de Montreal |
| MTVB Herons Basket | — | Montecatini Terme | — | — |