The transmitter at Wrotham, Kent brings digital radio services to around 133,000 people and improves the coverage for a further 7.6 million across London, north Kent and Surrey.
Listeners in these areas will be able to enjoy the corporation's digital-only stations, such as 6 Music and Radio 7, alongside commercial stations available on the DAB platform.
"The BBC is committed to broadening the availability of digital radio and we are delighted to further expand and improve coverage in the South East and London," said Mark Friend, controller of multiplatform & interactive at BBC Audio & Music.
"We hope more listeners will discover the range of programmes offered over DAB including ball-by-ball commentary of The Ashes on 5 Live Sports Extra and some great festive highlights on Radio 7, 1Xtra and 6 Music over Christmas."
The BBC is currently investing in more than 60 extra DAB transmitters to fulfil its Royal Charter commitment to bring digital radio to 90% of the UK by next year. Coverage currently stands at around 88% of the population.
However, the corporation has faced criticism from the commercial radio industry that not enough money is being invested in the DAB platform as digital radio takeup slows.
In September, Global Radio founder Ashley Tabor told the BBC to "put their money where their mouth is" by improving the UK's digital radio network.
Tabor said that his company, which owns the Heart, Capital, Classic FM and LBC stations, would hold back investment in new digital services until the DAB platform has a comparable reach to analogue FM.
Selected commercial radio groups have also refused to promote digital radio services this Christmas until the BBC commits to increasing its investment in the underlying infrastructure.