In 1987, Kallas was one of the authors of the IME plan for self-managing Estonia with Tiit Made, Edgar Savisaar and Mikk Titma.

[2] Kallas entered politics in 1994 as one of the founders of liberal Estonian Reform Party.

He was twice appointed the Acting Commissioner for Economic and Monetary Affairs and the Euro in Olli Rehn's stead, from 19 April 2014 to 25 May 2014 while he was on electoral campaign leave for the 2014 elections to the European Parliament and from 1 July 2014 to 16 July 2014 after he took up his seat.

Kallas is married to doctor Kristi Kallas, who, during the Soviet deportations from Estonia, at age six months, was deported to Siberia with her mother and grandmother in a cattle car and lived there until she was 10 years old.

His daughter Kaja Kallas was the leader of the Reform party and was the prime minister of Estonia from 2021 to 2024.