Bermondsey & Old Southwark Labour MP Neil Coyle is to serve on the House of Commons Work & Pensions Select Committee.
Mr Coyle – elected to Parliament eight months ago – takes up a committee seat vacated by Emma Lewell-Buck MP.
Ms Lewell-Buck was recently promoted by Labour leader Jeremy Corbyn to be shadow communities minister.
He was elected unopposed to the committee position by members of the Parliamentary Labour Party.
Mr Coyle said: "The Department for Work & Pensions is already working on implementing a change in policy that I tabled during the Welfare Bill's committee stages which will benefit terminally ill people seeking help.
"They will get help worth about £1 million a year and more swiftly than existing help provides.
"It is great to have influenced legislation and policy from the Labour backbenches.
"I'll take this experience, plus over a decade working on social security issues, on to the Work & Pensions Select Committee and hopefully have even greater influence over issues affecting the daily lives of people across Bermondsey & Old Southwark."
The Bermondsey MP will continue to serve as parliamentary private secretary to Chris Bryant, shadow leader of the House of Commons.