His father Edward Vieth Sittler had been born a United States citizen, but shortly after Germany's September 1, 1939, invasion of Poland had applied for naturalisation as a German citizen, renouncing his United States Citizenship, and had worked for the Reich Ministry of Public Enlightenment and Propaganda, including as an English language commentator broadcasting propaganda intended to weaken the morale of allied personnel during the Second World War.

His father had an unsuccessful marriage in the United States before emigrating to Germany, and on September 27, 1940, had remarried to Walter Sittler's mother, Lily Margaret, who had been born in England in 1918 and held British and German citizenship.

[12] Sittler has spoken out against the Stuttgart 21 railway and urban development project, and against populist politics, saying in a 2016 interview:[13] Wir befinden uns ja derzeit in einer nicht ungefährlichen Situation.

Wenn wir weiterhin eine freie Gesellschaft haben wollen, müssen die Leute endlich aufstehen und sich dafür engagieren.

Populism doesn't get us any further).In the 2016 United States presidential election he voted for Hillary Clinton against Donald Trump (another American-born television personality of German and British ancestry).