His wife, Anna Courtney-Forsyth, whom he met when she worked as a senior account manager at Publicis, also passed away later in hospital.
Adam Kean, a creative director at Publicis, who worked with Courtney, said: "Keith was an incredibly loquacious character - he had a tremendous amount of energy. He was hugely loved here and he knew everybody."
Courtney studied at art school in Belfast, where his finals work was bought by the Ulster Museum. His first job was at Gold Greenlees Trott, followed by three years at WCRS, where he created a series of campaigns for Carling Black Label.
During a long and illustrious career, he later worked at Simons Palmer Denton Clemmow & Johnson, where he created campaigns including Nike's "it's not the winning, it's the taking apart".
He also spent time at Lowe Howard-Spink, was the creative director at K Advertising and worked at Leagas Shafron before moving to Publicis in 1998, where he worked until 2006. After leaving, he lived in Cornwall, where he was restoring an old church.
The funeral and memorial service will be next week in Cornwall. For more details on both, contact David Balko at DraftFCB on 020 3048 0000 or e-mail firstname.lastname@example.org.
Add your own tribute to Keith's contribution to UK advertising at www.brandrepublic.com/campaign/courtney.