A list of parliamentary opposition leaders in the Canadian province of Ontario, from 1867 to the present.

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• Archibald McKellar (L) 1867-1869 (not formally recognized as opposition leader; led Liberals in legislature)

#	Name	Party	Took Office	Left Office
1.	Edward Blake	Liberal	December 1869	December 1871
2.	Matthew Crooks Cameron	Conservative	December 1871	1878
3.	William Ralph Meredith	Conservative	October 1878	October 1894
4.	George Marter	Conservative	October 1894	April 1896
5.	James Whitney	Conservative	April 1896	January 1905
6.	George William Ross	Liberal	February 1905	January 1907
7.	George P. Graham	Liberal	January 1907	August 1907
8.	Alexander MacKay	Liberal	August 1907	1911
9.	Newton Wesley Rowell	Liberal	December 1911	1917
10.	William Proudfoot	Liberal	February 1918	October 1919
11.	Hartley Dewart	Liberal	1919	October 1921
12.	Wellington Hay	Liberal	March 1922	June 1923
13.	William Sinclair 1	Liberal	August 1923	June 1934
14.	George Henry	Conservative	July 1935	December 1938
15.	George Drew	Conservative/Progressive Conservative	1939	1943
16.	Ted Jolliffe	CCF	August 1943	June 1945
17.	Farquhar Oliver	Liberal	July 1945	June 1948
-	Ted Jolliffe (second time)	CCF	July 1948	November 1951
-	Farquhar Oliver 2 (second time)	Liberal	1951	April 1958
18.	John Wintermeyer	Liberal	April 1958	August 1963
-	Farquhar Oliver 3 (third time)	Liberal	October 1963	September 1964
19.	Andrew Thompson	Liberal	September 1964	November 1966
20.	Robert Nixon	Liberal	February 1967	October 1975
21.	Stephen Lewis	NDP	October 1975	June 1977
22.	Stuart Smith	Liberal	June 1977	September 1981
-	Robert Nixon 4 (second time)	Liberal	January 25, 1982	February 21, 1982
23.	David Peterson	Liberal	February 1982	June 1985
24.	Frank Miller	Progressive Conservative	1985	1985
25.	Larry Grossman	Progressive Conservative	1985	1987
26.	Bob Rae	NDP	1987	1990
-	Robert Nixon 4 (third time)	Liberal	1990	1991
27.	Murray Elston 5	Liberal	1991	1991
28.	Jim Bradley 6	Liberal	1991	1992
29.	Lyn McLeod	Liberal	1992	1996
30.	Dalton McGuinty	Liberal	1996	2003
31.	Ernie Eves	Progressive Conservative	2003	2004
32.	Bob Runciman 7	Progressive Conservative	2004	2005
33.	John Tory	Progressive Conservative	2005

(1) From 1930 the Liberal Party was led by Mitchell Hepburn but Sinclair continued as Leader of the Opposition as Hepburn did not seek a seat in the legislature until the 1934 general election which made him Premier.

(2) Until 1954 the Liberals were led from outside the legislature by Walter Thomson with Oliver as acting Leader of the Opposition. Oliver led the party in his own right (for a second time) from 1954 until 1958.

(3) Interim Leader of the Opposition following the personal defeat of Wintermeyer in the 1963 provincial election until Thompson's election as leader.

(4) Interim leader of the party and Opposition following the personal defeat of Premier David Peterson in the 1990 Ontario election.

(5) Elston became interim leader when Nixon from the legislature to accept a federal appointment. Elston stepped down in November when he decided to be a candidate at the Liberal Leadership Convention.

(6) Interim leader between resignation of Elston and election of McLeod.

(7) John Tory was chosen as leader of the Ontario Progressive Conservative Party on September 18, 2004, but did not hold a seat in the legislature. On September 28 the party announced that Bob Runciman would act as interim Leader of the Opposition until Tory enters the legislature. Tory was elected to represent Dufferin--Peel--Wellington--Grey on March 17 2005 and was sworn in as an MPP later that month.