Founder, arranger and singer of such a cappella groups as SixPäck and Cash-n-go. Besides his live performances he has worked in TV broadcasting as an arranger and singer for the a cappella background music in the weekly Die allerbeste Sebastian-Winkler-Show (Best of Sebastian Winkler Show, Bavarian Broadcasting) and the Einsfestival. In 2011 he founded the pop choir Greg is Back, which won the International Choral Competition in Budapest, the Bavarian Choral Competition and took second place at the German Choral Competition in Weimar. Nearly all the arrangements for Greg is Back are written by Martin Seiler himself. In addition, he is also a freelance coach for choirs.