Jo Stevens will leave the post of Secretary of States for Wales as Andy Burnham prepares to unveil his prime ministerial team.
Cardiff East MP Stevens made the announcement on X, saying she was “proud” of her role in government.
Stevens had faced criticism from some Welsh Labour politicians for not supporting more powers for the Welsh government.
But she said Wales saw its biggest budget settlement for public services in the history of devolution while she was in office.
It is not known who will be replacing Stevens.
Meanwhile, First Minister Rhun ap Iorwerth said the new Welsh secretary must be “someone who respects and wants to see devolution work”.
He said he had not yet had a conversation with Burnham, but plans were in place for one.
Ap Iorwerth added he hoped a new prime minister would be “an opportunity for a reset” in the Cardiff-London relationship.
He said Sir Keir Starmer did not take much interest in devolution or Wales.
But he added he hoped the relationship with Burnham would be better as he had a background “of understanding and appreciating the value of devolution”.
