Shavanah Taj has been appointed acting general secretary of trade union umbrella body TUC Wales.
It comes after Martin Mansfield has taken up a secondment with Welsh Government, joining the new Social Partnership & Fair Work Directorate.
Ms Taj joins Wales TUC from the Public and Commercial Services Union (PCS), where she has been Welsh secretary since 2013.
She is the second woman to hold the role, following Felicity Williams who was general secretary from 2004 to 2008, and the first from a black, Asian and minority ethnic background.
TUC Wales represents 48 affiliated unions with a total membership of 400,000 workers across Wales.
The three biggest unions on membership Wales are Unite, Unison and the GMB.
Ms Taj said: “This is a great honour. Never has a strong, organised, responsive trade union movement been so needed.
“This feels like a critical time for our movement. Brexit and the impact of climate change and automation are just a few of the major issues that will impact working people’s and families’ lives. We need to be a strong, loud, collective voice to make sure we get the best possible outcomes.
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“And it’s also a really exciting time. We’re making sure that people are better protected at work than ever before through guidance and agreements on tackling sexual harassment, non-guaranteed hours, combating the far right and creating menopause-aware workplaces.
“Welsh Government will also be taking forward social partnership legislation that will offer genuine protections for workers’ rights and delivering on the recommendations of the Fair Work Commission, which we fully support. This will place trade unions and collective bargaining at the heart of fairer work in Wales.”
TUC general secretary Frances O’Grady said: “We’re delighted that Shavanah is stepping into the leadership of the Wales TUC.
“I’ve known Shavanah a long time. She will put her heart and soul into winning for working families in Wales, cracking down on insecure contracts and making work fairer for everyone.
“At a time when growing our movement is more important than ever, she will bring the intelligence, passion and integrity that working people need."
Ms Taj, who lives in Cardiff, is married with two young children aged six and eight.