She was educated in a Catholic convent in Günzburg and later attended school in Georgia and Virginia after her family relocated to the United States in 1959.

She studied political science at the School of International Service at American University (Washington, D.C.), from which she graduated in 1970 with a bachelor's degree.

While working at the European Commission (Brussels, Belgium, 1971–83), Kelly participated in numerous peace and environmental campaigns in Germany and other countries.

[citation needed] After working for two years at the European Commission, she moved to an administrative post at the Economic and Social Committee, where she championed women's rights.

In 1982, Gerhard Schröder wrote a contribution in Die Zeit for the book Prinzip Leben, edited by Kelly and Jo Leinen, which discussed ecological problems and a possible nuclear war.

[3][4] In October 1983, Erich Honecker, the leader of the German Democratic Republic, met Petra Kelly, Gert Bastian and other Greens.

She demanded the release of all prisoners of the East German peace movement and asked Honecker why he repressed something in the GDR which he supported in the West.