[6] His favorite fish species are European bass,[10] Pollock,[11] Cod,[12] Thornback ray and Turbot[13] Guillaume was born in Boulogne-sur-Mer, France.

[15] In 2005 and 2006, he spent a few months in New Caledonia tracking tropical catches and releasing then[16] about fishing and a number of articles since 2005.

He writes article about fishing every month, especially in the "Pêche en Mer" French magazine.

He participates in Atlantic bluefin tuna tagging programmes with IFREMER and Spanish scientists[22] In 2007, he became product manager and team manager[23] for a French brand named "Sakura", where he developed rods, reels and lures for the European lure market.

As a sport fisherman, Guillaume is sponsored by April Marine, Beneteau and Simrad Yachting[25]