In 1984, he began working as a forester. He also worked as a dairy farmer. In 2001, he was a Left Party leader in Pajala and continued working, as a forestry machine driver. He spoke in support of the party's feminist program. By 2005, he was a member of the Pajala Municipal Council. In 2012, he was elected to represent Norbotten County on the Left Party's board alongside . Shortly after his election in 2014, Lahti became a party spokesperson for energy and business policy. He advocated for
LKAB to take over
Northland Resources after the latter declared bankruptcy and the future of the
Kaunisvaara mine became uncertain. During his first term in the Riksdag, he was involved with the
Committee on Industry,
Committee on Transport, and the
Committee on Environment and Agriculture. In 2021, it was announced that he would be the new rural policy spokesperson for the Left Party. During the lead-up to the
2022 election, he spoke about finding a balance between working towards a future of renewable energy without crippling Northern Swedish economies (as they still rely heavily on forestry, diesel, and gasoline). In 2023, he expressed support for , an effort to produce steel without carbon dioxide in Norbotten. As of March 2025, he was also working as the Left Party's energy policy spokesperson. He voiced opposition to legislation financing four large-scale nuclear reactors, in an effort to achieve net zero emissions by 2045. == Personal life ==