Cardiff Arms Park is the latest sport stadium in Wales to support the National Health Service.
The venue, used by Cardiff Blues, will provide a staff welfare centre, catering facilities and headquarters for the Dragon's Heart Hospital.
The hospital, which is within the Principality Stadium, will have up to 2,000 beds to fight the coronavirus.
"As soon as we were aware of the plans we offered the entire Arms Park," said Blues chief executive Richard Holland.
"Our operations team have been working tirelessly with colleagues at the WRU, Principality Stadium and the local health board and the Arms Park has now been transformed.
"These are uncertain and unprecedented times but we are proud to be able to support the NHS by making our facilities available."
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The Arms Park is currently providing logistical support during the building of the facility.
The first phase was completed over Easter weekend, and the hospital will open its doors to the first 350 patients in the upcoming days.
Cardiff and Vale University Health Board Chief Executive Len Richards said: "I'd like to thank the Welsh Rugby Union, Cardiff Council and Cardiff Blues for their commitment to the Ysbyty Calon y Ddraig Hospital.
"We have never undertaken a project this big before and in such a short space of time.
"Please help us to help those who need our hospitals the most by staying home, washing your hands and heeding the clinical advice to keep you and your families safe."
A field hospital is also being converted at the WRU training facility at The Vale Resort, which will provide 290 extra beds.
Parc y Scarlets in Llanelli, Carmarthenshire, is being converted to offer 350 extra beds. This includes setting up bays with electricity and plumbing, as well as access to catering from stadium kitchens.
Work has started at the Llandarcy sports academy in Neath Port Talbot, normally used by the Ospreys rugby squad as a training base and by local students. It will be completed in the next few weeks with 340 beds in use.
Testing centre drive-throughs have also been set up at Cardiff City Stadium and Newport's Rodney Parade.