Arnold was born on 11 January 1959 in Herdtlinsweiler, a suburb of Schwäbisch Gmünd in Weiler in den Bergen.

[2][3] Arnold was awarded a postgraduate scholarship from the German Council of the European Movement to study abroad at the College of Europe in Bruges.

[7] In July 2013 Arnold partnered with Deutsche Bahn to recruit African refugees to work for the railway.

Arnold continued his commitment to find work for refugees in Germany, employing 60 asylum seekers to help with the State Garden Show in 2014 and later with the Festival Europäische Kirchenmusik.

He declined to run for the office of Minister-President, instead announcing he would seak re-election as Lord Mayor of Schwäbisch Gmünd in October of that year.

In February 2020 Arnold was considered as a top candidate for the Christian Democratic Union in the mayor election for Stuttgart but ultimately decided to decline the party's offer.

[13] In July 2020 Arnold met with Sir Stephen Houghton, a British government official and head of the Barnsley Metropolitan Borough Council, via video conferences to offer support and advice for handling the COVID-19 pandemic.

[14][15] On 21 July 2020 Arnold, along with Boris Palmer and Matthias Klopfer, wrote a letter to Baden-Württemberg Minister-President Winfried Kretschmann and Minister of the Interior Thomas Strobl about riots affecting their towns.