Connolly was born in Edinburgh, Scotland to Irish emigrant parents. He left school for working life at the age of 11, but despite this start to life he would become one of the leading left-wing theorists of his day.
He is believed to have joined the British Army at the age of 14, and was stationed in Dublin where he would meet his wife. By 1896 he had left the army and established his Irish Republican Socialist Party (IRSP).
While active as a Socialist in britain Connolly was among the founders of the Socialist Labour Party which split from the British Socialist Party in 1903.
His legacy in Ireland is mainly due to his contribution to the nationalist cause and his leftism has been largely overlooked (although there is a present day IRSP which claims his legacy). In Scotland his thinking was hugely influential to socialists such as John Maclean, who would similarly combine his leftist thinking with nationalist ideas when he formed his Scottish Workers Republican Party.