McGuinness, who was understood to have been suffering from a rare heart condition for some time, died on Tuesday according to several media outlets.

He became deputy first minister of Northern Ireland in 2007, and served alongside three Democratic Unionist Party leaders - Ian Paisley, Peter Robinson and, most recently, Arlene Foster.

McGuinness, who quit as deputy first minister in January, had worked at the center of the power-sharing government that was formed in the wake of the 1998 Good Friday Agreement, with briefs including that of education minister.

Born in Derry, Northern Ireland, McGuinness was radicalized at a time of bitter sectarian division in the province and rose to become second-in-command of the Irish Republican Army (IRA) at the age of 21.

Read: Northern Ireland torn between past and future

Sinn Fein President Gerry Adams paid tribute to his former colleague in a statement. "Throughout his life Martin showed great determination, dignity and humility, and it was no different during his short illness," said Adams.

"He was a passionate republican who worked tirelessly for peace and reconciliation and for the re-unification of his country. But above all he loved his family and the people of Derry and he was immensely proud of both."

A major figure during five decades of conflict and peace, McGuinness had announced in January 19 that he would leave politics altogether, allowing someone else to lead his nationalist party into elections earlier this month. He gave illness as the reason.

Green energy collapse

McGuinness' resignation and the withdrawal of the Irish nationalist Sinn Fein from the government came as a response to a bungled green energy program involving DUP leader and first minister, Arlene Foster.

Collapse of the government at Stormont meant led to a March 2 election in which Sinn Fein made major gains against the DUP, with the two parties currently in political deadlock. If the dispute is not settled, the British government could either impose direct rule of Northern Ireland from London, or new elections could be called.

Michelle O'Neill - McGuinness' successor in Northern Ireland - has called for a referendum on unification of north and south in light of the election results and Britain's decision to leave the European Union.

Read: Crisis in Northern Ireland as Brexit looms

rc/jm (AFP, Reuters)