He has been a Member of the Legislative Assembly of the Australian Capital Territory since 2016 when he was elected as the Labor Party representative for the newly formed electorate of Yerrabi.

[9] In Pettersson's inaugural speech he highlighted growing intergenerational inequality, the importance of education, and the dangers of casualisation in the workforce.

[10] Pettersson has campaigned for more light rail services[11] and the expansion of the popular Canberra e-scooters to his electorate of Yerrabi.

In September 2018, Pettersson introduced a historic bill to decriminalise the possession and personal use of small amounts of cannabis in the ACT.

[16] Under this proposed legislation certain drugs such as MDMA, cocaine, methamphetamine and heroin would be decriminalised in small quantities for personal use and possession.