The vehicles, which come in various sizes, will distribute post from the central London depot.
They were produced by Oxfordshire-based carmaker Arrival, which recently opened a new factory in Banbury.
Another batch of 100 electric vans for Royal Mail has also been ordered from Peugeot.
Having already been trialled by Royal Mail, these will enter service in December.
Arrival says the nine vehicles it has supplied come in sizes of three and a half, six and seven and a half tonnes.
Although the current prototype versions of the vans are fitted with wing mirrors, a spokeswoman for Arrival told the BBC they will be removed from the final design - as cameras will be used to monitor traffic to the rear instead.
Royal Mail was "delighted" to be collaborating with Arrival, said Paul Gatti, Royal Mail Fleet's managing director.
"We will be putting them through their paces over the next several months to see how they cope with the mail collection demands from our larger sites," he added.
Royal Mail's fleet comprises about 49,000 vehicles in total.
"European postal providers, starting with DHL in Germany, have been taking this approach for a while now," said Ananth Srinivasan, a mobility expert with research consultancy Frost & Sullivan.
He added that five countries - the UK, Germany, France, Italy and Spain - had the potential to convert significant proportions of their fleets to electric vehicles in the coming years.
"Our research indicates that by 2025 these countries may have 100,000 postal service vehicles going electric between them," he told the BBC.
Royal Mail is beginning trials in London of nine fully electric vans with ranges of up to 100 miles.