Thomas Kiefer grew up in Perl/Mosel and initially studied church music at the Saar University of Music (choral conducting: Andreas Göpfert, orchestral conducting: Max Pommer), supplemented by numerous masterclasses (with John Scott, Stefan Parkman, among others). Fascinated by the Swedish choral tradition, he took up a two-year postgraduate course in choral conducting in Anders Eby's class at the Royal College of Music in Stockholm in 2003, which had a lasting impact on him. In autumn 2004, Thomas Kiefer won first prize at the 3rd International Competition for Young Choral Conductors in Vienna and the special prize of the Vienna Singverein.
In September 2005, he joined Trier Cathedral as cathedral cantor and was entrusted with the direction of the young choir work: initially the children's and youth choir, later the cathedral boys‘ and girls’ choir (until October 2016). Since September 2013, he has had overall responsibility for the choral and orchestral music at what is considered Germany's oldest cathedral.
He has lectured at the Saar University of Music, for Europa Cantat and other choral organisations. He was particularly involved as a member of the executive committee of the German choral association Pueri Cantores and was responsible for the 5th German Choral Festival Pueri Cantores in 2015 as artistic director and project manager with 3,000 young people from 100 choirs.
On 1 October 2016, Thomas Kiefer was appointed Professor of Choral Conducting at the University of Music and Performing Arts Vienna.