The Duke of Cambridge's praise came during a series of phone and video calls.
During the call - made on 17 March with Dr Thelma Craig, a respiratory consultant at the Mater Hospital - William said: "I just want to say on behalf of everyone what a fantastic job you've done. You've all held it together and been absolutely wonderful people.
"It's been a real team effort but we're all very proud of you.
"The NHS has gone from already being much loved to probably the most admired organisation around.
"Thank you so much for all your hard work."
As well as speaking to people by phone and video calls, the duke has in recent weeks also visited vaccination centres in King's Lynn and Westminster.
Kensington Palace said that since the start of the year the duke has spoken to more than 300 staff and volunteers spanning the breadth of the NHS workforce across the UK.William's office said he wanted to check in on the wellbeing of all those supporting the NHS, and to thank them for the vital part they are playing in the UK's response to the COVID-19 pandemic.