| Magika Pallacanestro | — | Castel San Pietro Terme | — | — |
| Magnolia Basket Campobasso | — | Campobasso | 2017 | — |
| Mariscal Miller | Copa Peru | — | — | Estádio Jorge Basadre |
| Mariscal Nieto de Ilo | Copa Peru | — | — | Estadio Mariscal Nieto |
| Mariscal Sucre | — | — | 1925 | Estádio Nacional do Peru |
| Maurolico Messina | — | — | — | — |
| Memphis Grizzlies | National Basketball Association | Memphis | 1995 | Pyramid Arena, FedExForum |
| Mens Sana Basket | Liga Italiana de Basquetebol | Siena | 1861 | Palasport Mens Sana |
| Mercede Basket Alghero | — | Alghero | 1977 | — |
| Meyana Mesagne | — | Mesagne | — | — |
| Miami Marlins | Major League Baseball | — | 1993 | LoanDepot Park, Hard Rock Stadium |
| Miguel Grau de Abancay | Copa Peru | — | 1955 | Estadio Monumental de Condebamba |
| Milwaukee Braves | Major League Baseball | Milwaukee | 1953 | Milwaukee County Stadium |
| Milwaukee Brewers | Major League Baseball | 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 | Major League Baseball | — | 1901 | Target Field, American League Park, Metropolitan Stadium, Hubert H. Humphrey Metrodome, Boundary Field, Griffith Stadium |
| Minnesota United FC | Major League Soccer | Minneapolis | 2015 | Allianz Field, TCF Bank Stadium |
| Minnesota Vikings | National Football League | Minnesota | 1961 | Metropolitan Stadium, TCF Bank Stadium, Hubert H. Humphrey Metrodome, U.S. Bank Stadium |
| Minnesota Wild | — | Saint Paul | 2000 | Grand Casino Arena |
| Miraflores Sporting Club | — | — | — | Estadio Nacional del Perú (1897) |
| Modena Basket | — | — | — | — |
| Montigarda Basket | — | Montichiari | — | — |
| Montreal Expos | Major League Baseball | — | 1969 | Estádio Olímpico de Montreal, Jarry Park Stadium |
| Montreal Maroons | — | — | 1924 | Montreal Forum |
| MTVB Herons Basket | — | Montecatini Terme | — | — |