The 3rd Parliament of Ontario was in session from 18 January 1875 until 25 April 1879, following the 1875 general election in which the Liberal Party was returned as the majority party. Oliver Mowat was again the province's Premier.

The Ontario Liquor Licence Act, 1876 (often referred to as the Crooks Act),39 Victoria, 3. 26; R.S.O. 1877, c. 181 which transferred control of licenses for the sale of alcohol from individual municipalities to commissioners appointed by the province, was passed.

Rupert Mearse Wells served as speaker for the assembly.

Members of the Assembly RidingMemberPartyFirst elected / previously electedNo. of termsCommentsAddingtonHammel Madden DerocheLiberal18712nd termAlgomaSimon James DawsonLiberal18751st termMember until 26 August 1878. Resigned to enter federal politics.Robert Adam Lyon (1878)Liberal18781st termWon byelection, was member from 16 September 1878.BrantHugh FinlaysonLiberal18673rd termBrant SouthArthur Sturgis HardyLiberal18732nd termProvincial Secretary and Registrar in Mowat ministry after March 19, 1877BrockvilleWilmot Howard ColeLiberal18751st termBruce NorthDonald SinclairLiberal18673rd termBruce SouthRupert Mearse WellsLiberal18722nd term SpeakerCardwellJohn FlesherConservative18751st termCarletonGeorge William MonkConservative18712nd termCornwallAlexander Fraser McIntyreConservative18751st termServed 18 January 1875 – 18 June 1875. Election disqualified on 8 June 1875, courts ordered byelectionJohn Goodall Snetsinger (1875)Liberal1872, 18752nd term*Defeated McIntyre in byelection 17 July 1875 and served to end of Parliament session.DufferinJohn BarrConservative18751st termDundasAndrew BroderConservative18751st termDurham EastJohn RosevearConservative18751st termDurham WestJohn McLeodLiberal1867, 18723rd term*Elgin EastJohn Henry WilsonLiberal18712nd termElgin WestM.G. MunroeConservative18751st termMember until June 1875 when he was unseated in election trial.Thomas Hodgins (1875)Liberal1871, 18752nd term*As opponent of Munroe, he won the seat upon conclusion of an election trial. Resigned in 1878 to become a candidate for federal politics.David McLaws (1878)Liberal18781st termWon byelection and served from September 1878 until end of Parliament session.Essex NorthJames Colebrooke PattersonConservative18751st termMember until September 1878 when he resigned to enter federal politics.Solomon White (1878)Conservative18781st termWon byelection and was member after September 1878.Essex SouthLewis WigleConservative18751st termFrontenacPeter GrahamConservative18751st termDied in office in January 1877.Delino Dexter Calvin (1877)Conservative1868, 18773rd term*Won byelection in 1877 and served to end of Parliament session.GlengarryAlexander James GrantIndependent-Liberal18751st termGrenville SouthChristopher Finlay FraserLiberal18722nd termProvincial Secretary and Registrar in Mowat ministry until July 23, 1875? Commissioner of Public Works in Mowat ministry after March 24, 1874Grey EastAbram William LauderConservative18673rd termGrey NorthThomas ScottConservative18673rd termDisqualified in September 1875.Scott was banned for 8 years from holding any municipal or provincial office, or from voting in a provincial election. David Creighton (1875)Conservative18751st termWon byelection and was member from 1 November 1875.Grey SouthJames Hill HunterLiberal18751st termHaldimandJacob BaxterLiberal18673rd termHaltonWilliam BarberLiberal18673rd termMember until 30 June 1875 after he was unseated in election trial.William Durie Lyon (1875)Liberal18751st termWon byelection and was member from 15 November 1875 until end of Parliament session.Lyon was voted Reform candidate for this riding on 4 October 1875.HamiltonJames Miller WilliamsLiberal18673rd termHastings EastNathaniel Stephen ApplebyIndependent-Conservative18751st termHastings NorthGeorge Henry BoulterConservative18673rd termHastings WestThomas WillsConservative18751st termHuron EastThomas GibsonLiberal18712nd termHuron SouthArchibald BishopLiberal18732nd termHuron WestAlexander McLagan RossLiberal18751st termKent EastArchibald McKellarLiberal18673rd termCommissioner of Agriculture and Public Works in Mowat ministry until 25 July 1875 when he retired from politics.Daniel McCraney (1875)Liberal18751st termWon byelection in 1875 and was member until end of Parliament session.Kent WestAlexander CouttsConservative18751st termKingstonWilliam RobinsonLiberal18712nd termLambton EastPeter GrahamLiberal18751st termLambton WestTimothy Blair PardeeLiberal18673rd termCommissioner of Crown Lands in Mowat ministryLanark NorthWilliam MostynConservative18751st termLanark SouthAbraham CodeConservative18693rd termLeeds North and Grenville NorthHenry MerrickConservative18712nd termLeeds SouthRobert Henry PrestonConservative18751st termLennoxJohn Thomas GrangeConservative18712nd termLincolnSylvester NeelonLiberal18751st termLondonWilliam Ralph MeredithConservative18722nd termLeader of Opposition after c. October 1878Middlesex EastRichard TooleyConservative18712nd termMiddlesex NorthJohn McDougallConservative18751st termMiddlesex WestJohn WatterworthLiberal18722nd termMonckHenry Ryan HaneyLiberal18722nd termMember until 18 November 1878, having died in office.Richard Harcourt (1878)Liberal18781st termWon byelection and was in the Legislature as of January 1879 until the end of the Parliament session.Muskoka and Parry SoundJohn Classon MillerLiberal18751st termNorfolk NorthJohn Fitzgerald ClarkeLiberal18712nd termNorfolk SouthRichard RichardsonConservative18751st termNorthumberland EastJames Marshall FerrisLiberal18751st termNorthumberland WestWilliam HargraftLiberal18751st termOntario NorthThomas PaxtonLiberal18673rd termOntario SouthNicholas W. BrownConservative18751st termOttawaDaniel John O'DonoghueLiberal18742nd termOxford NorthOliver MowatLiberal18722nd term Premier and Attorney General in Mowat ministryOxford SouthAdam OliverLiberal18673rd termMember until 15 July 1875 after he was unseated by election trial.Adam Crooks (1875)Liberal1871, 18752nd term*Won byelection in 1875 and was in the Legislature as of December 1875. He served until the end of the Parliament session.; new election called in August 1875. Treasurer in Mowat ministry until March 19, 1877; Minister of Education in Mowat ministry after February 19, 1876PeelKenneth ChisholmLiberal18732nd termPerth NorthDavid Davidson HayLiberal18751st termPerth SouthThomas BallantyneLiberal18751st termPeterborough EastJohn C. O'SullivanConservative18751st termAlthough unseated by election trial on 2 August 1875, he retained this riding.Peterborough WestGeorge Albertus CoxLiberal18751st termUnseated in election trial 2 August 1875.William Hepburn Scott (1875)Conservative1874, 18752nd term*Won byelection and was member from December 1875.PrescottWilliam HarkinConservative18751st termPrince EdwardGideon StrikerLiberal18712nd termRenfrew NorthThomas DeaconConservative18712nd termRenfrew SouthJames BonfieldLiberal18751st termRussellAdam Jacob BakerConservative18751st termSimcoe EastJohn KeanConservative18751st termSimcoe SouthD'Arcy Edward BoultonConservative18732nd termDied in office 16 February 1875.William McDougall (1875)Independent-Liberal18751st termWon byelection and was member from 1 June 1875 to 9 September 1878. Resigned early to seek seat in federal House of Commons.William James Parkhill (1878)Conservative18781st termWon by-election and was member from 1 October 1878.Simcoe WestThomas LongConservative18751st termStormontJames BethuneLiberal18722nd termToronto EastMatthew Crooks CameronConservative18673rd termLeader of the Opposition until c. 1878. Served as member of legislative assembly until 9 January 1879 when he retired from politics.Alexander Morris (1878)Conservative18781st termWon byelection and was member from January 1879 until the end of Parliament session.Toronto WestRobert BellConservative18751st termVictoria NorthJohn David SmithLiberal18751st termWas member until 27 August 1875, after being unseated in election trial.Duncan McRae (1875)Conservative18751st termWon byelection.Victoria SouthSamuel Casey WoodLiberal18712nd termRetained seat in August 1875 byelection.Commissioner of Agriculture in Mowat ministry after July 23, 1875: Treasurer in Mowat ministry after March 19, 1877Waterloo NorthMoses SpringerLiberal18673rd termWaterloo SouthJohn FlemingLiberal18751st termDied in office 21 January 1877.Isaac Master (1877)Liberal18771st termWon byelection after recount and was member from March 1877.WellandJames George CurrieLiberal18712nd termWellington CentreCharles ClarkeLiberal18712nd termWellington SouthPeter GowLiberal18673rd termMember until 1876 when he resigned.James Massie (1876)Liberal18761st termWon byelection and was in the Legislature as of January 1877 until the end of the Parliament session.Wellington WestJohn McGowanLiberal-Conservative18742nd termWentworth NorthThomas StockConservative18751st termDisqualified in September 1875. Was Conservative member until 30 June 1875.Stock was banned for 8 years from holding any municipal or provincial office, or from voting in a provincial election. James McMahon (1875)Liberal18751st termWon byelection and was in the Legislature as of December 1875 until the end of the Parliament session.Wentworth SouthWilliam SextonLiberal18673rd termYork EastJohn LaneLiberal18751st termYork NorthJoseph Henry WiddifieldLiberal18751st termYork WestPeter PattersonLiberal18712nd term

Election trials The early months of this Parliament were marred by election trials in many ridings. Most of these cases challenged the validity of the election results on such charges as bribery or corruption. A common accusation was that of "treating", where candidates or their agents would buy potential electors alcohol or other favours.

The following ridings and candidates were affected: