Conservative support is centred in the interior of the riding, particularly in the upscale Lorne Park area, while the Liberals and the NDP tend to do better along the waterfront of the riding, such as Port Credit and Lakeview, and the eastern and western edges of the riding.
It consisted initially of the part of the City of Mississauga lying south of a line drawn from west to east along Highway 5, south along Cawthra Road, and east along the Queen Elizabeth Way.
In 1987, it was redefined to consist of the part of the City of Mississauga lying south of a line drawn from southwest to northeast along Dundas Street West, east along the Credit River, northeast along the Queen Elizabeth Way, northwest along Cawthra Road, and northeast along the Queensway East to the eastern city limit.
Map of the riding (1996 boundaries)
In 1996, it was redefined to consist of the part of the City of Mississauga lying south of a line drawn from southwest to northeast along Dundas Street West, southeast along Erin Mills Parkway, northeast along the Queen Elizabeth Way, northwest along Hurontario Street, northeast along the Queensway East to the northeastern city limit.
In 2003, it was given its current boundaries as described above.
In 2013, the riding gained the area around Huron Park, and was renamed Mississauga—Lakeshore. It was defined to consist of the part of the City of Mississauga lying southeast of a line drawn from northeast to southwest along the Queensway to Mavis Road, north along Mavis Road until Dundas Street and west along Dundas Street to the southwestern city limit.
Since the 2015 Canadian Federal election, the Liberal Party of Canada has succeeded in holding Mississauga-Lakeshore as they have done in 2015, 2019 and 2021 elections with significant margins over 45%. This trend is aligned with the continued Liberal Party of Canada's dominance of Greater Toronto Area politics and seats.
The Mississauga South riding and its precursors, while being more competitive than in provincial elections, still has a generally conservative history, and despite voting Liberal since 1993, could be described as a small "c" conservative riding. The Progressive Conservatives held the riding from creation its first election in 1979 under Don Blenkarn, (who served as MP for Peel South, one of the precursor ridings between 1972–1974), until 1993, when he was defeated by Paul Szabo. With the exception of the 1988 election, Szabo has been the Liberal candidate in all election between 1980 (an election he almost won) and 2011.
The riding voting Liberal in 1993 can in part be blamed by vote-splitting on the right, as Blenkarn was knocked into third place by the Reform Party candidate, although both were far behind Szabo, who only marginally improved on the Liberal performance from 1988, winning 37%, only 2% more than the 1988 Liberal result, and less than the combined vote total for the two right-wing parties. Szabo however greatly increased his percentage of the vote in the elections afterward, winning over 50% in every election from 1997–2004, despite facing a united right-wing vote in 2004.
In the 2006 election Szabo and the Liberals were re-elected again; however, the Liberal vote dropped sharply, with the Conservatives coming within 5% of winning the riding, getting 40% of the vote, one of the best performances for them in the Greater Toronto Area. The riding was generally assumed to be a top Tory target for the next election; however, the drawn out and somewhat acrimonious nature of the Conservative nomination process, and Szabo's increased profile as a result of his chairmanship of the House of Commons Ethics committee may have damaged Conservative attempts to capture the riding. Despite the Conservatives strengthening in the 2008 election overall, Arrison was unable to defeat Szabo, and Mississauga South was one of the few ridings outside Quebec where the Liberal Party increased the percentage of the vote received from 2006 (albeit very slightly).
From 2006 to 2015 the riding was held by the Conservatives, however, starting in 2015 as a part of the overall Liberal dominance of Greater Toronto Area seats and ridings, the riding has gone and stayed Liberal. Incumbent Sven Spengemann successfully defeated Conservative Stella Ambler in 2015 and 2019 and Conservative challenger Michael Ras in the 2021 snap election.