Marius, along with his lawyer Moira Meltzer-Cohen, has fought tirelessly for trans-prisoner rights. Marius came out as trans in 2014 and has fought for gender affirming care for himself and other prisoners for the past decade+. It is believed that he was the first trans masculine person to obtain transition-related health care after coming into federal custody, setting a precedent for others coming after him. 

In 2016, Marius, along with friends in the US and Australia, founded Jan 22: International Day of Solidarity with Trans Prisoners. Since 2016, the event has developed into an autonomous structure, with local groups organizing and collaborating how they see fit. These events have brought increased awareness and support for other trans prisoners such as Ky Peterson.

Marius, along with Moira and the group Trans Pride Initiative were part of a legal battle in TX to allow trans prisoners the right to a legal name change. This initiative has stalled, but Marius was able to achieve legal name change after his transfer to FCI Danbury in CT. While at Danbury, he fought and won the right to be transferred to a male prison.