Leanne Wood said she is looking "forward to the challenge” after accepting a new role in the Plaid Cymru Shadow Cabinet.
The Rhondda AM also said she will use her position as the Shadow Cabinet Secretary for Housing and Social Justice to “support and empower some of our most oppressed citizens.”
The portfolio also covers Regeneration & Equalities, which includes responsibility for welfare benefits and criminal justice, prisons, probation, courts and drugs.
The new role was allocated as part of a reshuffle of the roles Plaid Cymru AMs carry out under new leader Adam Price.
Reacting to the appointment, Ms Wood said: “I’m pleased to accept my new role within the Plaid Cymru team.
“It will provide a good opportunity to get involved with campaigns and policy work which can help, support and empower some of our most oppressed citizens.
“There will be plenty of challenges ahead with the changes in benefits and the deep problems in the criminal justice system and housing sector following a decade of cuts because of austerity.”
She added: “I will draw on my experience as a probation officer, youth worker and Women’s Aid worker & management board member (chair), in order to reach out to our communities and tackle the real problems they face. I look forward to the challenge."