Giannis Kleontas was born in Neapoli Thessaloniki in 1980. From the age of twelve he started his involvement with music. He studied at the University of Macedonia, in the traditional department, specializing in three-string bouzouki. He plays bouzouki, guitar, tamboura (sazi), tzoura, baglama, percussion.
He has been involved in music professionally since 1996. In 2009 he was Head of the Department of Folk and Traditional Music at the "Musique de la Renaissance" Conservatory of the Municipality of Oreokastro, Thessaloniki. During the period 2006-2007 he participated in concerts-tributes to Grigoris Bithikotsis and Stelios Kazantzidis with the orchestra of Christos Mitrentzis. In the period 2003-2005 he participated as leading bouzouki  in concerts-tributes, of the folk orchestra of the Municipality of Neapoli Thessaloniki, to the composers Mimi Plessas, Yiannis Spanos, Mikis Theodorakis, Vassilis Tsitsanis and Giorgos Zambetas led by Vangelis Liolios. From 2003 to 2015 he taught in the folk music-bouzouki classes at the conservatories "Musique de la Renaissance", "En Techni", "Classical Conservatory", "Bolero" of the Municipality of Thessaloniki.
He participated in bouzouki seminars with Nikos Tatasopoulos, Manolis Karantinis, Vangelis Trigas.
From 1996 until today he has collaborated with important artists such as: Petros Gaitanos, Marianthi Kefala, Elena Giannakaki, Giannis Floriniotis, Anneta Marmarinou, Kostas Kragelis, Sokratis Papaioannou, Dimitris Papaioannou, Maria Soultatou, Giannis Giannoulis, Manolis Mitsias, Eleni Tsaligopoulou, Christos Mastelos, Christos Petridis, Christos Thivaios, Penny Baltatzi, Andreas Karakotas et al. in live shows or in recordings. He was a founding member of the musical group "The 10 bouzouki of Domna" with which he has been performing since 2018. He participated in concerts with the SONE orchestra.

From the educational year 2023-24, Giannis Kleontas began collaborating with Thanasis Polykandriotis and the Philippos Nakas Conservatory - Thessaloniki branch.