St. Helens South and Whiston is a constituency created in 2010 represented in the House of Commons of the UK Parliament since 2015 by Marie Rimmer of the Labour Party.

Further to the completion of the 2023 Periodic Review of Westminster constituencies, the seat was subject to minor boundary changes, with parts of Whiston and Cronton ward being included in the new constituency of Widnes and Halewood, first contested at the 2024 United Kingdom general election.

[2] The predecessor seat of St Helens South was held by the Labour Party since the 1935 election.

The Liberal Democrats came second in 2010 with 22.2% of the vote; this has gradually declined and by the 2024 general election they came in sixth with 5.8%.

The Conservatives were relegated to fourth place in 2024 by independent candidate James Tasker.