Siegloch worked as a television journalist between 1973 and 2011, for German public broadcaster ARD from 1973 to 1988 and from 1988 to 2011 for ZDF.

His professional career began in 1973, as an editor at NDR, where he worked on the Tagesschau and on regional broadcasts; from 1982 to 1985, he also presented news magazine Tagesthemen.

Siegloch moved to ZDF in 1988, where he became head of the main editorial department for domestic affairs, working on such programmes as the Politbarometer.

From 2003 onwards, he was deputy editor-in-chief of ZDF, and head of the news department; alongside these duties, he presented Heute Journal between 2003 and 2007, acting as a regular substitute for Marietta Slomka and Claus Kleber.

From December 2008, he was head of the ZDF office in New York, responsible for reporting on Wall Street, the United Nations, and Canada.