Gruenewald was born in Sankt Polten in the state of Lower Austria. She was educated at a high school in Wieselburg and studied political science, philosophy and jurisprudence at the University of Wien, where she gained a doctorate in political science. She has spent her whole professional life in politics, either as an employee of the Democratic party or as a parliamentary representative. She was a senior research fellow in the economic policy department of the Lower Austria Chamber of Labour from 1990 to 1999.