Grossen was born in the town of Frutigen in the Canton of Bern. He apprenticed as an electrical planner and worked for a solar energy company. After the death of the company's owner, Grossen and a colleague were left in charge of the firm.[1]
He joined the Green Liberal Party, which was founded in 2007 and later opened a cantonal affiliate in Bern. In 2011, he ran for the National Council. Grossen was elected as the party increased its vote share to 5.4% with 12 seats.[2] In 2015, he was re-elected.
Grossen was named as a party vice president in 2016. In 2017, the party president, Martin Bäumle announced his intent to leave the post. Grossen was elected to succeed Bäumle.[3]
In the 2019 election, Grossen was re-elected and the Green Liberals increased the vote share to 7.8%, taking 16 seats.[4]
Grossen has advocated for the end of nuclear power in Switzerland.[5] He is a supporter of marriage equality. As part of his party's climate plan, Grossen supported
ending subsidies to cattle farmers to reduce meat consumption and increase payments to plant-based products.[6]
