after completing secondary school in 1978 at the theo-koch-schule in grünberg, hesse, lesch studied physics at the university of giessen, then at the university of bonn, where he completed his doctoral degree in 1987 and worked at the max-planck-institute for radio astronomy. from 1988 to 1991 he was a research assistant at the state observatory at heidelberg-königstuhl. in 1992 he was a visiting professor at the university of toronto. in 1994 he was habilitated at the university of bonn.