Lewisham East MP Heidi Alexander has been appointed shadow health secretary, replacing Andy Burnham, who is now shadow home secretary.
The appointment comes after Jeremy Corbyn was elected as the new leader of the Labour party at the weekend.
Under former Labour party leader Ed Miliband, Ms Alexander served as the party whip.
She has previously been Lewisham’s deputy mayor from 2006 to 2010 and its cabinet member for regeneration.
Ms Alexander led the Save Lewisham Hospital campaign almost three years ago, which opposed the closure of the hospital’s accident and emergency unit.
She has also been chair of the all party parliamentary group on choice at the end of life.
Following her appointment, Ms Alexander commented via social media platform Twitter: “Humbled to serve as shadow health secretary.
“The NHS is facing immense challenges and I will do all I can to hold this government to account,” she said.