Meanwhile, Eerdmans became active in local politics. From 2009 to 2014 he was an alderman of Capelle aan den IJssel on behalf of Livable Capelle. From 2014 to 2018 he was an alderman of the neighbouring city of Rotterdam on behalf of Livable Rotterdam. From 2018 to 2021 he was a municipal councillor and Livable Rotterdam group leader in this city.