Westerberg was born in Nyköping and graduated from Stockholm School of Economics in 1974. His family has been running a family business for generations and he is now the richest member of the Riksdag, with a personal wealth exceeding 200 million SEK, (around $30 million 2006). His brother, Lars Westerberg, was CEO of Autoliv.
Per Westerberg has been active within Moderate politics since the election campaign in 1966, when he joined the Moderate Youth League. In 1979, he was elected to the Riksdag for his home county of Södermanland; he is currently the longest-serving member of the Riksdag. During the Moderate-led government 1991-1994, Westerberg served as Minister for Industry and Trade.
In 2003 he was elected as first of the three Vice Speakers of the Riksdag, and on October 2, 2006 he was elected Speaker of the Riksdag by the new liberal-conservative majority.
On October 4, 2010 he was dramatically re-elected as Speaker of the Riksdag, by a 194-153 vote (with 20 votes in favor being from the Sweden Democrats, whose potential decisiveness to his re-election had been viewed as controversial).
Per Westerberg and his family continue to make their home in Nyköping and he continues to serve on the Board of the Moderate Party and as chairman of the Moderate Party in Södermanland.