From 1 March 2019, Northumbrian Water will source 30% of its electricity needs from the offshore project, completed in 2018.
The ten-year deal will see roughly 100GWh delivered to the company's activities annually. Ørsted said the PPA covers a "small percentage of the power" produced from the project.
It is the first offshore wind corporate PPA to be signed so far in the UK. Race Bank comprises 91 Siemens Gamesa Renewable Energy SWT-6.0-154 turbines, installed 32km off England's east coast.
"The long-term stability this brings is fantastic for us, and great news for our customers and stakeholders, because it reduces operational costs without compromising our work," said Northumbrian Water group commercial director Graham Southall.
The Danish firm said it would also provide a "balancing service of the wind output so that the electricity can be delivered to Northumbrian Water under their existing supply agreement" signed in 2018.
Race Bank is being supported by the UK's now-expired Renewables Obligation Certificates (ROC) scheme
"For Ørsted, this agreement is an important step towards building long-term green partnerships with corporate power customers, added Alana Kühne, Ørsted's head of corporate PPAs.
While the deal is the first of its kind in the UK, Vattenfall's Kriegers Flak offshore wind project in Denmark is also being supported by a corporate offtake deal.
Pharmaceutical company Novo Nordisk and biotechnology firm Novozymes signed a deal in July 2018 to purchase "approximately a fifth" of the energy produced from the 600MW site, when it is completed in 2021.
Kriegers Flak will be located in the Baltic Sea, 15km from the Danish coast. It will comprise 72 Siemens Gamesa SG 8.0-167 DD turbines.