He was born in Barcelona in 1973. At the age of eight years old he started his first tap dance lessons. He received several grants from the Generalitat de Catalunya to study tap dance in New York with dancers such as Brenda Bufalino, Barbara Duffy and Savion Glover, among others. In 1993 he won the first prize at the World Tap Dance Championship in Switzerland, organized by the IDO (International Dance Organization).
He has been part of the best tap dance companies in the United States, such as the American Tap Dance Orchestra, Manhattan Tap and The Tap Collective (New York), as well as Steps Ahead (Los Angeles), with whom he has performed throughout the United States and Europe.
In Spain, he has danced in the shows 'Keatoniana', 'New Orleans Jazz Tap' and 'Sax Tap'. He has danced and choreographed 'El Nas Vermell' and 'Scandal', and has performed at the 1999 Goya Awards ceremony with Rosa M. Sardà. He has been the organizer and host of the Tap Jams, weekly tap improvisation sessions that started at the Cova del Drac in Barcelona.
During the 2000-2001 and 2001-2002 seasons he was a solo tap dancer in the show 'Fire Of Dance' with which he toured around Poland, Germany, Austria, Italy, Sweden, Switzerland, Norway, Holland, Slovakia, Hungary and Belgium. During the month of September 2001 he performed on Broadway at the New Victory Theatre (New York) with the show 'La Vida Es Ritme', which he co-created with the company Camut Band. This same show has toured the festivals of Edinburgh (Scotland), Toronto (Canada), New Haven (USA), Greenwich (Great Britain) and Tàrrega (Spain). He has also choreographed and danced in the shows "Tap Olé", premiered in Chicago, and "Boogie Woogie Tap" with the "Lluís Coloma trio". He is the director of the company "Barcelona Rhythm Tap".
He is one of the few dancers who practice sand dance, with which he has gained international prestige and recognition. Guillem Alonso has been, as a teacher and organizer, the promoter of a new generation of tap dancers in Barcelona. Currently, he directs the Escola Luthier Dansa (Barcelona), where he organizes his Professional Tap Training open to dancers from all over the world. He has won the 2010 Dansacat Award in recognition of his professional career and in 2023 the Claqueta Award.