He was born in Thessaloniki in 1943. His career as a singer began in the early 1960s as a member of the band Trio Moreno, which started in Thessaloniki to become known in Greece, while also making a record trip from the USA. After the dissolution of the band, sometime in 1966, Kalatzis began his solo career and settled in Athens. There he began a collaboration with the famous composer George Mitsakis. His popularity began to grow and he had a productive collaboration with some of the most famous Greek composers of the period, such as Manos Loizos, Stavros Kougioumtzis, George Katsaros, Mimis Plessas and Giannis Spanos as well as singers such as Tolis Voskopoulos. Kalatzis also recorded appearances on albums with singers such as George Dalaras, Haris Alexiou, Giannis Parios, Mariza Koch, Litsa Diamanti and Costas Smokovitis, while he also appeared in ten movies performing his songs.
In the second half of the 1970s Kalatzis collaborated with the composer Nikos Karvelas. In 1981 he released an album of songs by Tolis Voskopoulos. His last album before retiring from active song was released in 1984, however in 1985 he took part in a big concert dedicated to the composer Manos Loizos that took place at the Olympic Stadium in Athens. In 2000 a double CD was released, the first containing some of his greatest hits in new releases and the second favorite Greek songs of other performers in his own performance. Kalatzis is considered one of the best singers of his time and several of his songs have been performed by younger singers.
In 2013, Giannis Kalatzis was honored in the Greek version of the TV program Your Face Sounds Familiar broadcast by ANT1 with the actor Konstantinos Kazakos impersonating him and performing one of his most famous songs, “Delfini dolphinaki”.
Giannis Kalatzis died on July 13, 2017 at the age of 74.