Eric Joyce, who represented the Falkirk constituency at Westminster until 2015, plans to set up an online campaign aimed at convincing those who voted No in the 2014 referendum to switch their allegiances.
The former army major previously backed the continuation of the union between Scotland and the rest of the UK.
In a blog posted on his personal website, Joyce said the Brexit vote in June had “fatally undermined” arguments against independence.
“Many of us voted No to independence because we were told – by UK politicians and EU officials alike – that remaining within the UK was our only hope of remaining EU citizens,” he said.
“Some of us actually were those very politicians!”
He argued many No voters were soft unionists who “just weren’t convinced the risk of independence was worth it”.
In a 2014 blog post, Joyce explained he was “a unionist in broad terms, but I’m finding the dishonesty and negativity of the ‘No’ campaign – the way it treats Scots like dummies – increasingly offensive.”
The 55-year-old resigned from the Labour party in 2012 after being found guilty of common assault following an incident in a House of Commons bar, in which he was alleged to have headbutted a Conservative campaigner.