[1][2] In 1948 he began teaching at the Berliner Hochschule für Musik.
He became acquainted with Boris Blacher, a composer with whom he collaborated extensively.
As harpsichordist, Hartig made numerous recordings, mostly in the role of continuo player rather than soloist.
His compositional output consists mainly of concertos, sonatas, songs, oratorios and choral works.
His students included Carlo Domeniconi and Roland Pfrengle.