[2] After attending Central College of Commerce, Glasgow, he studied at the University of Abertay in Dundee where he graduated with a BA (Hons) in European Business Management with Languages and latterly an MBA.

Stuart was elected as the MSP for Greenock & Inverclyde on 5 May 2016 with a 53.7% vote share and a majority of 8,230, becoming the first SNP member to win this constituency at the Scottish Parliament.

He has also been very vocal in his support for action to be taken against the rise of fixed-odds betting terminals, securing a victory in 2018 when the UK Government finally agreed to limit the maximum stake to £2.

At McMillan's request, Inverclyde Council agreed to invite former gamblers into secondary schools to speak to pupils about the dangers of gambling.

[14] In November 2020, McMillan condemned Liberal Democrat leader Willie Rennie for claims of "anti-English rhetoric" by the SNP during the COVID-19 pandemic.

McMillan, who was born in Cumbria, said: "As an English Scot I'd like to put on record my anger and disgust at the comments from Willie Rennie at the weekend.