The transaction, for which the price tag was not disclosed, is part of a push to prepare for a global roll-out of the pair's experimental vaccine that could be reviewed by regulators as early as next month, among the first in the Western world.
The facility in the German city of Marburg will be converted to be fully on stream in the first half of 2021 with an annual production capacity up to 750 million doses of the inoculation, based on the so-called messenger RNA (mRNA) technology.
The two companies were previously aiming to supply up to 100 million doses worldwide by the end of this year and an additional 1.3 billion doses by the end of 2021.
The new site, with its 300 staff that will join BioNTech, will allow for a larger 2021 output target but it is not yet clear by how much on balance, a company spokeswoman said.
The biotech firm said the facility will be one of the largest mRNA manufacturing sites in Europe, alongside two of BioNTech's existing vaccine production sites. Pfizer has at least four production sites in the United States and Europe, it added.
Separately, BioNTech said it expects that the experimental Covid-19 vaccine it is developing with Pfizer will be able to be stored at refrigerator temperatures for at least two weeks, seeking to allay concerns that the compound may have to be deep-frozen.
Speaking at an online media briefing on the purchase of an additional German production site, Chief Executive Ugur Sahin said tests have recently confirmed the genetic compound remains stable at 2 to 8 degrees Celsius for five days but he expects storability at those conditions to be two weeks or longer.
He added that a good vaccine should have an efficacy of at least 70% to 75% for it to quell the pandemic and that was also the yardstick that BioNTech had set itself.