Premier (party) | Period | Assem- blies | Elections (Riding) |
| | 1st | John Sandfield Macdonald (Liberal-Conservative) | Jul. 15, 1867 Dec. 20, 1871 | ... 1st | Designated Jul. 15, 1867 Elected Sep. 3, 1867 to a coalition[1] (Cornwall) |
| | 2nd | Edward Blake (Liberal) | Dec. 20, 1871 Oct. 25, 1872 | 2nd ... | Elected Mar. 21, 1871 (Bruce South) Resigned (moved to federal politics) Oct. 25, 1872[2] |
| | 3rd | Sir Oliver Mowat (Liberal) | Oct. 25, 1872 Jul. 21, 1896 | ... 3rd 4th 5th 6th 7th 8th ... | Designated Oct. 25, 1872 (Oxford North) Re-elected Jan. 18, 1875 (Oxford North) Re-elected Jun. 5, 1879 (Oxford North) Re-elected Feb. 27, 1883 (Oxford North) Re-elected Dec. 28, 1886 (Oxford North) Re-elected Jun. 5, 1890 (Oxford North) Re-elected Jun. 26, 1894 (Oxford North) Resigned (Retired) Jul. 21, 1896 |
| | 4th | Arthur Hardy (Liberal) | Jul. 21, 1896 Oct. 20, 1899 | ... 9th ... | Designated Jul. 21, 1896 (Brant South) Re-elected Mar. 1, 1898 (Brant South) Resigned (Retired) Oct. 20, 1899 |
| | 5th | Sir George William Ross (Liberal) | Oct. 20, 1899 Feb. 8, 1905 | ... 10th | Designated Oct. 20, 1899 (Middlesex West) Re-elected May 29, 1902 (Middlesex West) |
| | 6th | Sir James Whitney (Conservative) | Feb. 8, 1905 Sep. 25, 1914 | 11th 12th 13th 14th ... | Elected Jan. 25, 1905 (Dundas) Re-elected Jun. 8, 1908 (Dundas) Re-elected Dec. 11, 1911 (Dundas) Re-elected Jun. 29, 1914 (Dundas) Died in office Sep. 25, 1914 |
| | 7th | Sir William Hearst (Conservative) | Oct. 2, 1914 Nov. 14, 1919 | ... | Designated Oct. 2, 1914 (Sault Ste. Marie) |
| | 8th | Ernest Drury (Farmer) | Nov. 14, 1919 Jul. 16, 1923 | 15th | Elected Oct. 20, 1919 coalition[3] (Halton)[4] |
| | 9th | George Howard Ferguson (Conservative) | Jul. 16, 1923 Dec. 16, 1930 | 16th 17th 18th ... | Elected Jun. 25, 1923 (Grenville) Re-elected Dec. 1, 1926 (Grenville) Re-elected Oct. 30, 1929 (Grenville) Resigned (changed jobs) Dec. 16, 1930 |
| | 10th | George Stewart Henry (Conservative) | Dec. 16, 1930 Jul. 10, 1934 | ... | Designated Dec. 16, 1930 (York East) |
| | 11th | Mitchell Hepburn (Liberal) | Jul. 10, 1934 Oct. 21, 1942 | 19th 20th ... | Elected Jun. 19, 1934 (Elgin) Re-elected Oct. 6, 1937 (Elgin) Resigned (Retired) Oct. 21, 1942 |
| | 12th | Gordon Daniel Conant (Liberal) | Oct. 21, 1942 May 18, 1943 | ... ... | Designated Oct. 21, 1942 (Ontario) Resigned (Retired) May 18, 1943 |
| | 13th | Harry Nixon (Liberal) | May 18, 1943 Aug. 17, 1943 | ... | Designated May 18, 1943 (Brant) |
| | 14th | George Drew (Progressive Conservative) | Aug. 17, 1943 Oct. 19, 1948 | 21st 22nd 23rd ... | Elected Aug. 4, 1943 to a minority (High Park) Re-elected Jun. 4, 1945 (High Park) Re-elected Jun. 7, 1948 (none[5]) Resigned (Retired) Oct. 19, 1948 |
| | 15th | Thomas Kennedy (Progressive Conservative) | Oct. 19, 1948 May 4, 1949 | ... ... | Designated Oct. 19, 1948 (Peel) Resigned (Retired) May 4, 1949 |
| | 16th | Leslie Frost (Progressive Conservative) | May 4, 1949 Nov. 8, 1961 | ... 24th 25th 26th ... | Designated May 4, 1949 (Victoria) Re-elected Nov. 22, 1951 (Victoria) Re-elected Jun. 9, 1955 (Victoria) Re-elected Jun. 11, 1959 (Victoria) Resigned (Stepped down) Nov. 8, 1961 |
| | 17th | John Robarts (Progressive Conservative) | Nov. 8, 1961 Mar. 1, 1971 | ... 27th 28th ... | Designated Nov. 8, 1961 (London North) Re-elected Sep. 25, 1963 (London North) Re-elected Oct. 17, 1967 (London North) Resigned (Retired) Mar. 1, 1971 |
| 18th | Bill Davis (Progressive Conservative) | Mar. 1, 1971 Feb. 8, 1985 | ... 29th 30th 31st 32nd ... | Designated Mar. 1, 1971 (Peel North) Re-elected Oct. 21, 1971 (Peel North) Re-elected Sep. 18, 1975 to a minority (Brampton) Re-elected Jun. 9, 1977 to a minority (Brampton) Re-elected Mar. 19, 1981 (Brampton) Resigned (Retired) Feb. 8, 1985 |
| 19th | Frank Miller (Progressive Conservative) | Feb. 8, 1985 Jun. 26, 1985 | ... 33rd ... | Designated Feb. 8 1985 (Muskoka) Re-elected May 2, 1985 to a minority (Muskoka) Resigned (opposition parties sign The Accord)[6] Jun. 26, 1985 |
| | 20th | David Peterson (Liberal) | Jun. 26, 1985 Oct. 1, 1990 | ... 34th | Designated Jun. 26, 1985 to a minority (London Centre) Re-elected Sep. 10, 1987 (London Centre) |
| | 21st | Bob Rae (NDP) | Oct. 1, 1990 Jun. 26, 1995 | 35th | Elected Sep. 6, 1990 (York South) |
| 22nd | Mike Harris (Progressive Conservative) | Jun. 26, 1995 Apr. 14, 2002 | 36th 37th ... | Elected Jun. 8, 1995 (Nipissing) Re-elected Jun. 3, 1999 (Nipissing) Resigned (Retired) Apr. 15, 2002 |
| 23rd | Ernie Eves (Progressive Conservative) | Apr. 15, 2002 Oct. 22, 2003 | ... | Designated March 23, 2002 (Dufferin—Peel—Wellington—Grey) |
| | 24th | Dalton McGuinty (Liberal) | Oct. 23, 2003 Incumbent as at Dec. 16, 2009 | 38th 39th | Elected Oct. 2, 2003 (Ottawa South) Re-elected Oct. 10, 2007 (Ottawa South) |