Geraint was born in Stockport and attended William Hulme's Grammar School in Manchester, before winning a scholarship to study classics at Pembroke College, Oxford. At Oxford, he rowed for both Pembroke College and Oxford University, and was captain of both Pembroke and the Oxford Lightweights.
After graduating, Geraint worked for Logica in London, and co-authored a book on UNIX programming. In 1988, he joined Microsoft, spending several years in Seattle and Paris, and then working at the UK Development Lab in Hampshire, where he was architect and lead developer of DirectShow, the media framework in Windows 95 and Windows NT.
In 1996, Geraint moved to Anglesey, and spent the next 18 years working as a freelance consultant on digital video software. In 2014, Geraint was hired to write the video streaming framework for Periscope. When Periscope was acquired by Twitter in January 2015, he joined Twitter full-time, and was responsible for Twitter's Real Time Media Infrastructure. In 2016, he was presented with the St David's Award for Innovation and Technology by the Welsh Government for his work on Periscope.
Geraint resigned from Twitter in May 2022, and is returning to freelance consulting at GDCL.
Geraint is married and has three daughters and three grandchildren. He and Judy live in Anglesey, and have just recently lost their spaniel, Jack.