Dumbarton (Gaelic: Dùn Breatann) is a county constituency of the Scottish Parliament covering parts of the council areas of Argyll and Bute and West Dunbartonshire. Under the additional-member electoral system used for elections to the Scottish Parliament, it elects one Member of the Scottish Parliament (MSP) by the first past the post method of election. It is also one of ten constituencies in the West Scotland electoral region, which elects seven additional members, in addition to the ten constituency MSPs, to produce a form of proportional representation for the region as a whole.
The seat has been held continuously by Jackie Baillie of Scottish Labour since being first contested at the 1999 Scottish Parliament election.
The other nine constituencies of the West Scotland region are: Cunninghame North, Cunninghame South, Clydebank and Milngavie, Eastwood, Inverclyde, Paisley, Renfrewshire North and Cardonald, Renfrewshire West and Levern Valley, and Strathkelvin and Bearsden. The region covers the whole of the council areas of East Dunbartonshire, East Renfrewshire, Inverclyde, North Ayrshire, Renfrewshire, and West Dunbartonshire; and parts of the council areas of Argyll and Bute, East Ayrshire, and Glasgow.
The Dumbarton constituency takes in Helensburgh and Lomond from the Argyll and Bute council area and covers Dumbarton and the Vale of Leven in West Dunbartonshire. The rest of West Dunbartonshire is covered by the Clydebank and Milngavie. The rest of Argyll and Bute is covered by the Argyll and Bute constituency, which is within the Highlands and Islands electoral region.
The Dumbarton constituency was created at the same time as the Scottish Parliament, in 1999, with the name and boundaries of the existing Dumbarton constituency of the UK Parliament. Ahead of the 2005 United Kingdom general election the House of Commons constituencies in Scotland were altered, whilst the existing Scottish Parliament constituencies were retained. There is now longer any link between the two sets of boundaries. The constituency boundaries were reviewed and altered ahead of the 2011 Scottish Parliament election. In 2025, ahead of the 2026 Scottish Parliament election, a further review was undertaken: a very minor boundary change was made in the Old Kilpatrick area where the constituency borders the Clydebank and Milngavie constituency in order to align constituency and ward boundaries.
The electoral wards of Argyll and Bute Council and West Dunbartonshire Council used in the current creation of Dumbarton are:
Dumbarton is the only constituency in the Scottish Parliament to have voted Labour in every election in the devolved era. Ahead of the 2021 election, The Times profiled the seat:
Incumbent Jackie Baillie has cultivated a profile as a hard working local MSP, a reputation that has helped her retain the seat as the Labour Party has declined nationally. In the 2021 election there was speculation that the seat could vote SNP for the first time, but in the end, Baillie increased her majority from 109 to 1,483. The SNP candidate, Toni Giugliano, blamed his loss on pro-Union tactical voting, tweeting: "The Tory vote in Helensburgh went to Labour in extraordinary numbers to keep us out."