After military service and a successful apprenticeship as an insurance salesman, he studied communication, German and Politics in Münster, Vienna and Berlin.

On 2 August 2004 Sonneborn founded, along with other editors of Titanic, the satirical political party Die PARTEI, one of whose aims is to rebuild the Berlin Wall.

He regularly holds readings both solo and as part of the trio Titanic Boygroup, together with Thomas Gsella and Oliver Maria Schmitt who preceded Sonneborn as editor-in-chief.

After joining the European Parliament in 2014,[6] he had to quit his jobs at Spiegel Online and ZDF since both companies wanted to stay objective in presenting politics.

[7] In February 2023, Sonneborn was one of 69 first signatories of the Manifest für Frieden initiated by politician Sahra Wagenknecht and publicist Alice Schwarzer, which calls for a stop to arms deliveries to Ukraine and a ceasefire and peace negotiations with Russia.