Scottish Labour leader Anas Sarwar voted at his local polling station at Pollokshields Burgh Hall in Glasgow on Thursday morning.
Mr Sarwar is standing against First Minister Nicola Sturgeon in the Glasgow Southside constituency, which includes Pollokshields.
Ms Sturgeon has already voted by post but she will join SNP candidate Rosa Salih at Annette Street Primary School polling station in Govanhill, Glasgow, to lend her support and meet a Syrian family as they cast their ballots.
Scottish Greens co-leader Lorna Slater will vote at a primary school in Edinburgh, while her fellow co-leader Patrick Harvie will vote at a school in Glasgow.
Scottish Conservative leader Douglas Ross will vote in Moray, while Alba Party leader Alex Salmond cast his ballot in Strichen, Aberdeenshire.
Scottish Liberal Democrat leader Willie Rennie has already voted by post.