Born in 1954, Siebert studied physics in Frankfurt. After receiving his degree in 1985, he worked as a science journalist (including for the FAZ newspaper), wrote his first book and moved from Frankfurt to Hamburg. There he co-founded the graphics magazine PAGE in 1986, and ran it as editor-in-chief until 1991, when he moved to Berlin. In Berlin, Siebert initially worked for two years for FSI FontShop International, where he published the first FontFonts, FUSE and the FontBook. In 1993, he took over marketing for FontShop Deutschland and in 1996, organised the first TYPO design conference; he started the Fontblog in 2004, and then in 2011, Creative Morning Berlin, as well as the TYPO offshoots in London and San Francisco. TYPO Days followed a year later. Since the autumn of 2014, he has been responsible for the German-language marketing for Monotype GmbH.