She was born in Bratislava as the daughter of Hans Gmelin (d. 1991), who was mayor of Tübingen from 1954-1974. She studied history, economy, law and political science in Tübingen and Berlin. Since 1974, she has been admitted as a lawyer, first in Stuttgart, then in Berlin. Since 1992, she has lectured law at the Freie Universität Berlin, which granted her the title of honorary professor in 1995.
She joined the German Social Democratic Party (SPD) in 1965 and became a member of the Bundestag in 1972. She held several party offices in the 1980s and '90s, serving as deputy party chairman from 1988-97. From 1994-98 she was chairwoman of the "Rechtspolitik" working group and legal adviser to the SPD parliamentary group. In 1993, the SPD nominated her to fill the vacancy of vice-president of the Federal Constitutional Court, but in a nine-month filibuster, she was deemed "too political" by the conservatives, after which she abandoned this career step in favor of Jutta Limbach.
From 1998 to 2002, she served as Justice Minister in Gerhard Schröder's first cabinet, where she oversaw a number of controversial reform projects such as the reform of German citizenship legislation, the quasi-legalization of same-sex marriage, and the overhaul of the German Civil Code, the most invasive since its inception in 1900.
After comparing Bush to Hitler in a highly-publicized incident during Schröder's re-election campaign, in the context of the Iraq crisis, Däubler-Gmelin resigned from her post. In the newly elected Bundestag, she has since been chairman of the Committee on Consumer Protection and Agriculture.
Däubler-Gmelin is a member of several charitable and non-profit organizations. Since 1969, she has been married to Prof. Dr. Wolfgang Däubler, one of the most prominent experts on German labor law. They have two children.