The former BBC Northern Ireland political correspondent wrote five books including biographies of two of the key players in the Northern Ireland peace process John Hume and David Trimble.
During a high-profile career at the BBC for three decades, he was an investigative reporter on the Spotlight programme as well as being both London correspondent and political correspondent.
He covered the latter years of the Troubles, the peace process, the 1998 Good Friday Agreement and Brexit.
His journalism on the Spotlight documentaries 'The BlackCatch' and 'The Life and Death of an IRA Quartermaster' were recognised with a European Journalism Award in 1995 and Royal Television Society Award in 2001, respectively.
In 2005 he was named the Northern Ireland Journalist of the Year by the CIPR and was also part of the BBC Newsline team that reported on the death of Ian Paisley. The coverage was awarded an Irish Film and Television Award in 2015.
Although he suffered from an illness in recent years, he continued to work and to write.
As well as political books, he wrote about military history including Ireland's Call: Irish Sporting Heroes who fell during the Great War.
He was fanatical football supporter especially of his home-town team Ballymena United, where he was a season ticket holder.
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"We are all heartbroken but grateful for his life so well and fully lived."
Walker is survived by his wife Katrin, daughter Grace and sons Gabriel and Jack.