After majoring in political science at the University of Heidelberg and the University of Hamburg, he completed his studies in journalism on a scholarship from Munich's Institut zur Förderung publizistischen Nachwuchses. In 1990, after the fall of the Berlin Wall, he became one of the founding journalists of the newspaper Neue Presse/Express in Halle, East Germany.
In 1999, he was appointed managing editor of the Financial Times Deutschland newspaper, which launched in February 2000. In 2001 he joined Spiegel Online as managing editor. In 2008 he was appointed editor-in-chief of Spiegel Online. In 2010 he became editor-in-chief at the German news agency Deutsche Presse-Agentur. In 2013 he became editor-in-chief of Der Spiegel and Spiegel Online. In 2015 he joined the Swiss Media Company Ringier as Managing Director for Blick-Group.
Since January 2017 Büchner has been Chief Content Officer of Madsack Media Group in Hanover, one of the leading regional publishers in Germany. He also serves as Managing Director and Editor-in-Chief of the RedaktionsNetzwerk Deutschland (RND), the central Newsroom of Madsack Media Group. The RND is in charge of the national and international news coverage for Madsack’s own 15 Newspapers and 30 other papers in eight German states with a total daily circulation of 1.5 million copies.