Mims Davies has been named as the new junior minister in the Wales Office.
The Conservative MP for Eastleigh in Hampshire replaces Stuart Andrew, who left the Wales Office to replace Guto Bebb at the Ministry of Defence.
Aberconwy MP Mr Bebb resigned as a defence procurement minister in a Brexit row over the Customs Bill.
Ms Davies, who studied politics and international relations at Swansea University, will not be paid for the role.
She will combine it with her paid job as an assistant government whip, enforcing party discipline in votes in the House of Commons.
"I look forward to returning to Wales and taking on the role of parliamentary under secretary of state, continuing the work of my excellent predecessors," Ms Davies said.
Welcoming the appointment, Welsh Secretary Alun Cairns said the "fantastic MP" would be "putting her formidable skills to good use and playing a key role in the delivery of policies that further support the growth of the Welsh economy" at the Wales Office.