Nearly 1,600 people in England alone are expected to benefit from the immunotherapy drug.
Previously, the drug was available for a small group of people with advanced TNBC which had spread or could not be removed through surgery.
Now, the regulatory agency recommended the use of pembrolizumab for early TNBC patients who are high risk of recurrence or locally advanced TNBC that has not spread.
The drug will be administered along with chemotherapy to reduce the tumour size before surgery.
It will also be given alone as a post-surgery treatment.
NHS chief executive Amanda Pritchard said: “This is a hugely significant moment for women. The NHS has struck a new deal to roll out a potentially life-saving drug for patients suffering with the most aggressive form of breast cancer that has been traditionally very difficult to treat.
“It will give hope to those who are diagnosed, and prevent the cancer from progressing, allowing people to live normal, healthy, lives.”
The regulatory decision was based on the interim results obtained from the KEYNOTE-522 trial.
Scheduled to be completed in 2025, the study demonstrated that the combination of pembrolizumab with chemotherapy made more likely that early-stage TNBC would completely respond to treatment.
It also found that the addition of pembrolizumab to chemotherapy before surgery and after surgery with pembrolizumab alone increases the time before TNBC recurs or progresses.