After working as a pastor and later Secretary General of the German Protestant Kirchentag, she was, from 1999 to 2010, state bishop of the Evangelical Lutheran Church of Hanover. In 2002, she received an honorary doctorate from the University of Hannover. From 2009 to 2010, she was chairwoman of the Council of the Evangelical Church in Germany (EKD). From August to December 2010, she was a visiting professor at Emory University in Atlanta (USA). In the period from January 2011 to March 2012, she taught and conducted research as a visiting professor for ecumenism and social ethics at the Ruhr-Universität Bochum (Max Imdahl Visiting Professorship). From April 2012 to June 2018, she served as Ambassador of the EKD Council for the Reformation Jubilee 2017.

Margot Kässmann has been retired since July 2018 and is primarily devoted to the writing of books. In addition, she is involved in selected projects such as the international children’s aid organization Terre des hommes, the German Foundation for the World Population or the social street magazine Asphalt. Since April 2019, Margot Kässmann publishes the monthly magazine Mitten im Leben.