Sam was born and raised in Cardiff and works in charity communications. While a student, he helped run a successful campaign for the university to divest from arms companies. A strong supporter of Welsh independence, he has been on the board of Undod, a campaign for a progressive, independent future for Wales. In 2023 he chaired the ACORN Cardiff tenants' union, where he helped run campaigns for rent controls and for Cardiff Council to crack down on discriminatory practices by landlords.

Before returning home to Wales, he was a Green councillor in Oxford from 2013-17. During that time he campaigned for the county council to divest its pension fund from fossil fuels.