His unlikely journey took him from being second-in-command of the Provisionals in Derry to deputy first minister at Stormont. He forged such a good working relationship with former Democratic Unionist Party (DUP) leader Ian Paisley that they were dubbed “the Chuckle Brothers”.
But it was his more strained relationships with Mr Paisley’s successors, Peter Robinson and Arlene Foster, that led to continual difficulties at the top of the power-sharing executive. In recent months he has been plagued by ill health.
Announcing his resignation at Stormont, he appeared tired and gaunt.
He became deputy first minister of Northern Ireland on May 8 2007, with Mr Paisley becoming first minister, following the St Andrews Agreement and the assembly election. In June 2008 he was reappointed as deputy first minister to serve alongside Mr Robinson, who succeeded Mr Paisley as first minister.
Mr McGuinness has always acknowledged his IRA past. In 1972, at the age of 21, he was second-in-command of the IRA in Derry, a position he held at the time of Bloody Sunday, when 14 civil rights protesters were killed in the city by soldiers with the 1st Battalion, Parachute Regiment The following year he was convicted by the Special Criminal Court after being arrested near a car containing explosives and ammunition.
After his release, and another conviction in the Republic for IRA membership, he became increasingly prominent in Sinn Féin, eventually becoming its best known face after Gerry Adams. He was in indirect contact with British intelligence during the hunger strikes in the early 1980s, and again in the early 1990s.
In 1982, he was elected to the Northern Ireland Assembly at Stormont representing his home city of Derry. He was the second candidate elected after John Hume.
But as with all elected members of Sinn Féin and the SDLP, he did not take his seat.
Mr McGuinness became Sinn Féin’s chief negotiator in the negotiations that led to the Good Friday Agreement.
After the agreement was concluded, he was returned as a member of the assembly for the same constituency, and nominated by his party for a ministerial position in the power-sharing executive, where he became minister of education.
The Good Friday Agreement proved difficult to implement and was amended by the St Andrew’s Agreement in 2006. By now the DUP and Sinn Féin, once staunch enemies, were the two largest parties in the North.
However, after Mr Paisley’s retirement, relations soured between the two parties, finally leading to the crisis of the RHI scandal and Mr McGuinness’s resignation.