His comments came in response to a challenge issued by the Conservatives to guarantee that the post would not be abolished.
Mr Murphy has told MPs that the role was part of the devolution settlement and, despite speculation to the contrary, would remain.
But, he admitted, it would be a decision for Prime Minister Tony Blair.
His comments came in response to a challenge issued by the Conservatives to guarantee that the post would not be abolished.
The future of the title "secretary of state for Wales" featured prominently during the annual Welsh day debate in the Commons.
The Conservatives promised they would keep the role but would combine it with another cabinet post to reflect the changes brought by devolution.
Tory leader William Hague - a former Welsh secretary himself - has suggested it could be merged with roles such as leader of the House in an effort to create "smaller government".
Assurance
And he challenged Labour to offers similar guarantees.
Mr Murphy assured MPs there were no plans to change the role.
He said it had been part of the devolution settlement voted on by the people of Wales and was included in the Government of Wales Act.
But he admitted that the issue was a matter for the prime minister.
Speculation
The future of the post has been a subject for debate in all parties since most of the Welsh secretary's powers transferred to the National Assembly for Wales in 1999.
There had been speculation that the Tories would scrap the role if they won the election.
Whitehall insiders believe Tony Blair may merge the Welsh post with its equivalent in Scotland and Northern Ireland to create a new Department for the Nations, if Labour wins the next election.