The government has agreed that two experts will now sit with the judge investigating the Grenfell Tower fire, following pressure from campaigners.
They had called for a diverse panel to oversee proceedings, saying the inquiry risked being a “whitewash”.
Theresa May said those appointed will have the “breadth of skills and diversity of expertise” to examine the reasons behind the disaster.
The BBC’s Tom Symonds said the decision marked a government U-turn.
Judge Sir Martin Moore-Bick’s inquiry will start hearing evidence this month.
The Grenfell United group said the move had come about after lots of hard work.
The group, which represents survivors and the bereaved, said it would mean the inquiry could “get to the truth of why our community was not listened to when we raised concerns”.
Prime Minister Theresa May had previously rejected calls for additional panel members, he said.
Skills and expertise
The blaze, which ripped through the high-rise building in west London on 14 June last year, killed 71 people.
Downing Street said in a statement: “Today the prime minister has announced her decision to appoint an additional two decision-making members to the Grenfell Tower Inquiry panel.
“Given the scale and complexity of concerning issues that are emerging from the inquiry’s early investigations, the prime minister has a continuing duty to ensure that the inquiry always has the skills and expertise it requires for the challenges that lie ahead.”
The announcement comes as MPs prepare for a Commons debate on the Grenfell fire on Monday.