Käßmann was pulled over on Saturday evening after running a red light in the city centre, and was found to have a blood alcohol content of 1.54 per mill, public prosecutor Jürgen Lendeckel confirmed on Tuesday.
The bishop, who was operating a church vehicle, apparently smelled of alcohol, and police asked her to undergo a breathalyser test. Well over the legal limit, Käßmann was taken to a nearby police station for a blood test.
“I'm shocked at myself,” Käßmann told daily Bild. “I am aware of how dangerous and irresponsible drunk driving is. I will, of course, confront the legal consequences.”
A church spokesperson told news magazine Der Spiegel that Käßmann's blood alcohol content was 1.1 per mill, not 1.3 per mill as initially reported by Bild. The former is at the threshold of the legal limit, while the amount of 1.54 per mill as confirmed by the state prosecutor constitutes being “absolutely unfit to drive” according to German law.
Meanwhile Hannover police told the magazine that they had taken Käßmann's driver's license and begun an investigation into the matter.
Margot Käßmann became the first woman to lead the 25 million members of Germany's Protestant churches in October 2009 after the majority of the synod voted in her favour.
Käßmann has proposed a radical course of reform for the Evangelische Kirche Deutschland (EKD), which suffers from shrinking congregations and revenues. In addition to streamlining the clergy, she plans to increase the church's profile and improve strained relations with Catholics.
Käßmann is known as an outspoken, tolerant and humorous leader, having once said: “Crabby Christians are a contradiction in themselves.”
Since taking her leadership post she has called for Germany to withdraw its troops in Afghanistan, calling the military action there "unjustified."
In 2006 the mother of four was diagnosed with breast cancer, but has since recovered.
She also divorced her husband of 26 years in 2007, a decision that sparked initial reactions varying from “open criticism to the point of malice, contempt and hatred,” as she described it in a memoir published last September.
The EKD was founded in 1945 as a multi-denominational federation of Lutheran, Reformed, and United Protestant church bodies. After Germany's reunification, the EKD combined both East and West German Protestant churches in 1991.