Was awarded the first prize in the National Competition of Music for the Youth of the "Gemeentekrediet" in 1981 at the early age of seventeen as a pupil Monique Vigneron.
In May 1982 he became a prize winner of the Kiwanis competition in Alost.
Received his bachelor’s degree in the guitar class of Mr. Sundermann with great distinction at the Royal Conservatory of Music in Brussels in June 1984.
Furthermore he was awarded a bachelors degree of chamber music (also with great distinction) with Mr Van Lysebeth.
For his interpretation of Belgian music he won the first prize in the Willem Pelemans competition.
In September 1985 he won the International Guitar Competition in Mettman (Germany).
He came in second at the International Guitar Competition "Andres Segovia" in Granada in January 1988.
In the same year he was awarded his master degree of chamber music at the Royal Conservatory of Music in Brussels with distinction.
The following year this same degree was given for Guitar (this time with high distinction).
In September 1992 his first CD appeared. Together with fellow guitarist Stefaan Baert
he made his own arrangements of well-known pop songs. A number of these appeared regularly on the national radio.
On October third 1992 Geert Claessens was the second prize winner in the Third International Guitar Competition "Printemps de la Guitare 1992" of Brussels/Walcourt, a competition with the same appreciation as the Queen Elisabeth Competition for piano and violin.
He was also awarded the Sabam-prize of the best interpretation of the obligatory Belgian piece.
April 23rd 1993 was the day where he was awarded with unanimity of votes the first prize (Emilio Pujol) at the 15 th International Guitar Competition of Carpentras (France).
Geert Claessens received the third prize (November 1993) at the world-renowned Guitar Competition Viña del Mar (Chile).
On March 6 1994 Geert became the first prize winner of the International Guitar Competition Manuel M. Ponce held every four years in Mexico-City.
He has given numerous concerts in France, Poland, The Philippines, Spain,Germany, Greece, Chile, Costa Rica and Mexico.
Since 1986 Geert teaches at the academies of Oud-Heverlee and Tirlemont.