- Make (Years In Operation) – Plant
-
- Models
- Maibohm (1916-1922) – Racine, WI
- B-6
- Majestic (1925-1927) – Binghamton, NY
- No models named
- Marmon (1902-1933) – Indianapolis, IN
- 34
- 74
- Little Marmon
- 75
- 68
- 78
- 69
- 79
- Big Eight
- 70
- 88
- 8-125
- Sixteen
- Marquette (1930) – Flint, MI
- 30
- Martin (1928-1932) – Garden City, NY
- Dart
- Midget
- Victory
- Mathis (1931) – Lansing, MI
- No models named
- Maxwell (1913-1925) – Detroit, MI
- 25
- 25-C
- Mayfair (1925) – Boston, MA
- No models named
- McFarlan (1912-1928) – Connorsville, IN
- 90
- Twin-Valve Six
- Single-Valve Six
- Line Eight
- McLaughlin (1926) – Bangor, ME
- No models named
- Mercer (1910-1925) – Trenton, NJ
- 5
- 6
- Mercury (1920) – Cleveland, OH
- H
- Mercury (1939-1942) – Dearborn, MI
- 99A
- 09A
- 19A
- 29A
- Merit (1921-1922) – Cleveland, OH
- B
- B-C
- Meteor (1915-1930) – Piqua, OH
- No models named
- Meteor (1919-1922) – Philadelphia, PA
- Four
- Metropolitan ()1922-1923 – Kansas City, MO
- M-61
- M-41
- Metz (1909-1921) – Waltham, MA
- Master 6
- Milburn Electric (1914-1923) – Toledo, OH
- 27L
- Miller-Quincy (1922-1924) – Quincy, IL
- No models named
- Mitchell (1903-1923) – Racine, WI
- E-40
- F-40
- F-42
- F-50
- Moller (1920-1922) – Lewistown, PA
- Four
- Monitor (1915-1922) – Columbus, OH
- Six
- Monroe (1914-1923) – Indianapolis, IN
- S
- Moon (1905-1929) – St. Louis, MO
- Victory 6-48
- 6-58
- 6-42
- 6-68
- 6-40
- 6-75
- 6-50
- A
- 6-60
- 6-72
- 8-80
- Murray (1916-1929) – Boston, MA
- Superb Six
- Six
- Models
