Born in Wattwil (St. Gallen), Brunner was first elected to the federal parliament in 1995 at the age of 21, as the youngest member ever.

[1] In addition to working on his farm, he operated an internet radio station aimed at farmers, and chaired the St. Gallen section of his party.

On 1 March 2008, Brunner succeeded Ueli Maurer as chairman of the national party.

[1] Brunner is close to the party's figurehead, Christoph Blocher, who serves as one of several vice chairmen.

[1] In January 2016, soon after the 2015 federal election, where the Swiss People's Party received record gains, Brunner announced that he would step down as the president of the SVP in April.