In 2003, 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 the Credit River, west along the Credit River, and southwest along Dundas Street West to the southwestern city limit.

Once one of the strongest bastions of PC support in the province (winning 61% of the vote as recently as 1999), and certainly in the Toronto area, Mississauga South provincially has become more and more Liberal in last election cycles, which can be attributed to the demographics of Mississauga South changing, with more socially-liberal-minded young families moving from Toronto into the area, and increasing ethnic populations which are usually Liberal friendly. Prior to Tim Peterson's very narrow upset victory in 2003 (despite a Liberal landslide province-wide, most pundits had predicted PC incumbent Margaret Marland would hold on to the seat), the area had not voted Liberal provincially since Confederation, and the PCs generally held the riding fairly easily (with some exceptions such as the 1987 election, which the PCs won by less than 1000 votes). The riding was one of the most watched in the 2007 election, as it was expected to be one of the closest races in the province. The voters, however, differed from expectations, handing Liberal Charles Sousa a more than 5000-vote victory, as the PC vote fell almost 9% from 2003, which many viewed as a rejection of the automatic installing of floor-crossing Tim Peterson as the PC candidate. The Liberals and particularly the Green Party received the benefit of angry PC voters, seeing a 3% and a 6% rise in voting percentage, respectively.

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