Liberal Democrat assembly member Jenny Randerson has taken her seat in the House of Lords.
The new Baroness Randerson of Roath Park took the oath in English and Welsh.
The Cardiff Central AM was supported by Lib Dem peer Lady Walmsley and cross-bench peer Lady Finlay of Llandaff.
A former Welsh Assembly Government culture minister, she will start work as a full-time peer after stepping down as an AM at May's election.
She was made a life peer in November alongside former Plaid Cymru leader Dafydd Wigley and former Labour MEP Eluned Morgan.
A former further education college lecturer, Baroness Randerson was a councillor in Cardiff before being elected to the assembly in 1999.
She served as a minister in the coalition assembly government with Labour between 2000 and 2003.
She said: "When I become a full-time baroness in April it will be my priority to fight Wales' corner on a range of issues as sometimes I often feel that there is a poor understanding of devolution in the Westminster village.
"The issues that I have promoted in the Bay will continue to be important to me in the House of Lords.
"My top priority will be to use every opportunity to emphasise the need for investment in Welsh jobs and the Welsh economy."