| Player | Pos | Seasons | Born | Birthplace | |
| Ken MacKenzie | P | 1965 | Mar 10, 1934 | Gore Bay | CN |
| Mike Madden | P | 1983-86 | Jan 13, 1957 | Denver | CO |
| Mike Maddux | P | 2000 | Aug 27, 1961 | Dayton | OH |
| Dave Magadan | 3B | 1995 | Sep 30, 1962 | Tampa | FL |
| Mike Magnante | P | 1997-98 | Jun 17, 1965 | Glendale | CA |
| Jim Mahoney | SS | 1965 | May 26, 1934 | Englewood | NJ |
| Gary Majewski | P | 2010 | Feb 26, 1980 | Houston | TX |
| Martín Maldonado | C | 2018-21 | Aug 16, 1986 | Naguabo | PR |
| Rob Mallicoat | P | 1987, 1991-92 | Nov 16, 1964 | St. Helens | OR |
| Jim Mann | P | 2001-02 | Nov 17, 1974 | Brockton | MA |
| Félix Mantilla | 3B/1B/2B | 1966 | Jul 29, 1934 | Isabella | PR |
| Kirt Manwaring | C | 1996 | Jul 15, 1965 | Elmira | NY |
| Tommy Manzella | SS | 2009-10 | Apr 16, 1983 | Chalmette | LA |
| Jake Marisnick | OF | 2014-19 | Mar 30, 1991 | Riverside | CA |
| Mike Marshall | P | 1970 | Jan 15, 1943 | Adrian | MI |
| Francis Martes | P | 2017 | Nov 24, 1995 | Cotui | DR |
| Corbin Martin | P | 2019 | Dec 28, 1995 | Houston | TX |
| Tom Martin | P | 1997 | May 21, 1970 | Charleston | SC |
| David Martínez | P | 2013-14 | Aug 4, 1987 | Cumana | VZ |
| Fernando Martínez | OF | 2012-13 | Oct 10, 1988 | Rio San Juan | DR |
| J.D. Martinez | OF | 2011-13 | Aug 21, 1987 | Miami | FL |
| Marty Martínez | SS/OF/3B | 1969-71 | Aug 23, 1941 | La Habana | CU |
| Pedro Martínez | P | 1995 | Nov 29, 1968 | Villa Mella | DR |
| Seth Martinez | P | 2021 | Aug 29, 1994 | Peoria | AZ |
| Roger Mason | P | 1989 | Sep 18, 1957 | Bellaire | MI |
| Eddie Mathews | 1B/3B | 1967 | Oct 13, 1931 | Texarkana | TX |
| T.J. Mathews | P | 2002 | Jan 9, 1970 | Belleville | IL |
| Ron Mathis | P | 1985, 1987 | Sep 25, 1958 | Kansas City | MO |
| Phil Maton | P | 2021 | Mar 25, 1993 | Paducah | KY |
| Dave Matranga | 2B | 2003 | Jan 8, 1977 | Orange | CA |
| Kazuo Matsui | 2B | 2008-10 | Oct 23, 1975 | Higashi-Osaka | JP |
| Justin Maxwell | OF | 2012-13 | Nov 6, 1983 | Olney | MD |
| Derrick May | OF | 1995-96 | Jul 14, 1968 | Rochester | NY |
| Lee May | 1B | 1972-74 | Mar 23, 1943 | Birmingham | AL |
| Milt May | C | 1974-75 | Aug 1, 1950 | Gary | IN |
| John Mayberry | 1B | 1968-71 | Feb 18, 1949 | Detroit | MI |
| Cameron Maybin | OF | 2017 | Apr 4, 1987 | Asheville | NC |
| Lee Maye | OF | 1965-66 | Dec 11, 1934 | Tuscaloosa | AL |
| Jack Mayfield | SS/2B/3B | 2019-20 | Sep 30, 1990 | Del Rio | TX |
| Edwin Maysonet | 2B/3B/SS | 2008-09 | Oct 17, 1981 | Arecibo | PR |
| Brian McCann | C | 2017-18 | Feb 20, 1984 | Athens | GA |
| Chas McCormick | OF | 2021 | Apr 19, 1995 | West Chester | PA |
| Lance McCullers, Jr. | P | 2015-18, 2020-21 | Oct 2, 1993 | Tampa | FL |
| Jeff McCurry | P | 1999 | Jan 21, 1970 | Tokyo | JP |
| Joe McEwing | 2B | 2006 | Oct 19, 1972 | Bristol | PA |
| Leon McFadden | SS/OF | 1968-70 | Apr 26, 1944 | Little Rock | AR |
| Terry McGriff | C | 1990 | Sep 23, 1963 | Fort Pierce | FL |
| Collin McHugh | P | 2014-19 | Jun 19, 1987 | Naperville | IL |
| Tony McKnight | P | 2000-01 | Jun 29, 1977 | Texarkana | AR |
| Bo McLaughlin | P | 1976-79 | Oct 23, 1953 | Oakland | CA |
| Mark McLemore | 2B | 1991 | Oct 4, 1964 | San Diego | CA |
| Mark S. McLemore | P | 2007 | Oct 9, 1980 | Sacramento | CA |
| Don McMahon | P | 1962-63 | Jan 4, 1930 | Brooklyn | NY |
| Craig McMurtry | P | 1995 | Nov 5, 1959 | Temple | TX |
| Rusty Meacham | P | 2000 | Jan 27, 1968 | Stuart | FL |
| Louie Meadows | OF | 1986, 1988-90 | Apr 29, 1961 | Maysville | NC |
| Dave Meads | P | 1987-88 | Jan 7, 1964 | Montclair | NJ |
| Román Mejias | OF | 1962 | Aug 9, 1930 | Abreus | CU |
| Mark Melancon | P | 2010-11 | Mar 28, 1985 | Wheat Ridge | CO |
| Mitch Meluskey | C | 1998-2000, 2003 | Sep 18, 1973 | Yakima | WA |
| Mike Mendoza | P | 1979 | Nov 26, 1955 | Inglewood | CA |
| Denis Menke | SS/2B/1B | 1968-71, 1974 | Jul 21, 1940 | Bancroft | IA |
| Orlando Merced | OF/1B | 2001-03 | Nov 2, 1966 | Hato Rey | PR |
| Roger Metzger | SS | 1971-78 | Oct 10, 1947 | Fredericksburg | TX |
| Brian Meyer | P | 1988-90 | Jan 29, 1963 | Camden | NJ |
| Jake Meyers | OF | 2021 | Jun 18, 1996 | Omaha | NE |
| Dan Miceli | P | 2003-04 | Sep 9, 1970 | Newark | NJ |
| Jason Michaels | OF | 2009-11 | May 4, 1976 | Tampa | FL |
| Matt Mieske | OF | 1999-2000 | Feb 13, 1968 | Midland | MI |
| Larry Milbourne | 2B/SS | 1974-76 | Feb 14, 1951 | Port Norris | NJ |
| Wade Miley | P | 2019 | Nov 13, 1986 | Hammond | LA |
| Norm Miller | OF | 1965-73 | Feb 5, 1946 | Los Angeles | CA |
| Orlando Miller | SS | 1994-96 | Jan 13, 1969 | Changuinola | PN |
| Trever Miller | P | 1998-99, 2006-07 | May 29, 1973 | Louisville | KY |
| Wade Miller | P | 1999-2004 | Sep 13, 1976 | Reading | PA |
| Blas Minor | P | 1997 | Mar 20, 1966 | Merced | CA |
| John Mizerock | C | 1983, 1985-86 | Dec 8, 1960 | Punxsutawney | PA |
| Dave Mlicki | P | 2001-02 | Jun 8, 1968 | Cleveland | OH |
| Brian Moehler | P | 2003, 2007-10 | Dec 31, 1971 | Rockingham | NC |
| Randy Moffitt | P | 1982 | Oct 13, 1948 | Long Beach | CA |
| Rafael Montalvo | P | 1986 | Mar 31, 1964 | Rio Piedras | PR |
| Aurelio Monteagudo | P | 1966 | Nov 19, 1943 | Caibarien | CU |
| Rafael Montero | P | 2021 | Oct 17, 1990 | Higuerito | DR |
| Ray Montgomery | OF | 1996-98 | Aug 8, 1969 | Bronxville | NY |
| Scott Moore | 3B/1B/OF | 2012 | Nov 17, 1983 | Long Beach | CA |
| Colin Moran | 3B/1B | 2016-17 | Oct 1, 1992 | Port Chester | NY |
| Omar Moreno | OF | 1983 | Oct 24, 1952 | Puerto Armuelles | PN |
| Joe Morgan | 2B | 1963-71, 1980 | Sep 19, 1943 | Bonham | TX |
| Al Morman | P | 1996 | Jan 6, 1969 | Rockingham | NC |
| Charlie Morton | P | 2017-18 | Nov 12, 1983 | Flemington | NJ |
| Andy Mota | 2B | 1991 | Mar 4, 1966 | Santo Domingo | DR |
| James Mouton | OF | 1994-97 | Dec 29, 1968 | Denver | CO |
| Jerry Mumphrey | OF | 1983-85 | Sep 9, 1952 | Tyler | TX |
| Pete Munro | P | 2002-04 | Jun 14, 1975 | Flushing | NY |
| Eric Munson | C | 2006-07 | Oct 3, 1977 | San Diego | CA |
| Rob Murphy | P | 1992 | May 26, 1960 | Miami | FL |
| Iván Murrell | OF | 1963-64, 1967-68 | Apr 24, 1943 | Almirante | PN |
| Joe Musgrove | P | 2016-17 | Dec 4, 1992 | El Cajon | CA |
| Brett Myers | P | 2010-12 | Aug 17, 1980 | Jacksonville | FL |